diff --git a/.github/workflows/test-domain-ntlm.yml b/.github/workflows/test-domain-ntlm.yml
new file mode 100644
index 00000000..aaa0b1ff
--- /dev/null
+++ b/.github/workflows/test-domain-ntlm.yml
@@ -0,0 +1,19 @@
+name: Domain NTLM regressions
+on:
+  push:
+    branches: ['**']
+  pull_request:
+  workflow_dispatch:
+permissions:
+  contents: read
+jobs:
+  test:
+    runs-on: windows-latest
+    strategy:
+      matrix:
+        shell: [powershell, pwsh]
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - name: Test domain NTLM policy without changing host settings
+        shell: ${{ matrix.shell }}
+        run: ./tests/DomainNtlm.Tests.ps1
diff --git a/WELA.ps1 b/WELA.ps1
index a5e00cd6..9244b2c7 100644
--- a/WELA.ps1
+++ b/WELA.ps1
@@ -451,6 +451,12 @@ function AuditLogSetting {
         }
     }
 
+    $domainNtlm = Get-WelaDomainNtlmState
+    $auditResult += [WELA]::new(
+        "NTLM Authentication", "Domain NTLM auditing", $domainNtlm.Description, @(),
+        "Not configured", "Enable all (7) on domain controllers only", "",
+        "AuditNTLMInDomain; applicability is determined from Win32_OperatingSystem.ProductType."
+    )
     $auditResult | ForEach-Object { $_.CountByLevel() }
 
     $auditResult | ForEach-Object {
@@ -978,6 +984,90 @@ function UpdateRules {
     }
 }
 
+function Get-WelaDomainNtlmState {
+    # ProductType distinguishes an actual DC from a member server with AD DS tools installed.
+    $state = [pscustomobject]@{
+        Applicable = $false
+        Readable = $false
+        Value = $null
+        Description = 'Unknown (computer role could not be determined)'
+    }
+    try {
+        $os = Get-CimInstance -ClassName Win32_OperatingSystem -Property ProductType -ErrorAction Stop
+        switch ($os.ProductType) {
+            1 { $state.Description = 'Not applicable (Windows client)'; return $state }
+            2 { $state.Applicable = $true }
+            3 { $state.Description = 'Not applicable (member or standalone server, including non-DC AD CS)'; return $state }
+            default { return $state }
+        }
+    } catch {
+        $state.Description = "Unknown (computer role query failed: $($_.Exception.Message))"
+        return $state
+    }
+    try {
+        $path = 'HKLM:\SYSTEM\CurrentControlSet\Services\Netlogon\Parameters'
+        $state.Description = 'Not configured'
+        if (Test-Path -LiteralPath $path -ErrorAction Stop) {
+            $properties = Get-ItemProperty -LiteralPath $path -ErrorAction Stop
+            $property = $properties.PSObject.Properties['AuditNTLMInDomain']
+            if ($null -ne $property) {
+                $state.Value = $property.Value
+                $state.Description = switch ($state.Value) {
+                    0 { 'Disabled (0)' }
+                    7 { 'Enable all (7)' }
+                    default { "Value $($state.Value) (not interpreted as Enable all)" }
+                }
+            }
+        }
+        $state.Readable = $true
+    } catch {
+        $state.Description = "Unknown (domain NTLM registry read failed: $($_.Exception.Message))"
+    }
+    return $state
+}
+
+function Set-WelaDomainNtlmAudit {
+    [CmdletBinding(SupportsShouldProcess = $true)]
+    param ([switch]$Auto)
+    $state = Get-WelaDomainNtlmState
+    Write-Host "Domain NTLM auditing: $($state.Description)"
+    if (-not $state.Applicable) {
+        Write-Host '[SKIPPED] Domain NTLM policy is only changed on a confirmed domain controller.' -ForegroundColor Yellow
+        return
+    }
+    if (-not $state.Readable) {
+        throw 'Domain NTLM policy was not changed because its current state could not be read.'
+    }
+    if ($state.Value -eq 7) {
+        Write-Host '[SKIPPED] Domain NTLM auditing is already Enable all (7).' -ForegroundColor Yellow
+        return
+    }
+    $path = 'HKLM:\SYSTEM\CurrentControlSet\Services\Netlogon\Parameters'
+    if (-not $PSCmdlet.ShouldProcess("$path\AuditNTLMInDomain", 'Set domain NTLM auditing to Enable all (7)')) { return }
+    if (-not $Auto) {
+        $response = Read-Host "Change domain NTLM auditing from '$($state.Description)' to 'Enable all (7)'? (Y/n)"
+        if ($response -ne '' -and $response -ne 'Y') {
+            Write-Host '[SKIPPED] Domain NTLM auditing.' -ForegroundColor Yellow
+            return
+        }
+    }
+    try {
+        if (-not (Test-Path -LiteralPath $path -ErrorAction Stop)) {
+            New-Item -Path $path -Force -ErrorAction Stop | Out-Null
+        }
+        Set-ItemProperty -LiteralPath $path -Name AuditNTLMInDomain -Value 7 -Type DWord -ErrorAction Stop
+        $after = Get-WelaDomainNtlmState
+        if (-not $after.Applicable -or -not $after.Readable -or $after.Value -ne 7) {
+            throw "Read-back did not confirm Enable all (7). Observed: $($after.Description)"
+        }
+        Write-Host '[OK] Domain NTLM auditing: Enable all (7), registry value verified.' -ForegroundColor Green
+        Write-Host 'Group Policy or MDM may reapply a different value; validate events on the domain controller.'
+    } catch {
+        throw "Domain NTLM configuration failed: $($_.Exception.Message)"
+    }
+}
+
+
 function Set-RegistryConfig {
     # レジストリを変更するため -WhatIf / -Confirm に対応する
     [CmdletBinding(SupportsShouldProcess = $true, ConfirmImpact = 'Medium')]
@@ -1294,11 +1384,12 @@ function ConfigureAuditSettings {
     Write-Host ""
     $regPaths = @(
         @{Path = "HKLM:\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0"; Name = "RestrictSendingNTLMTraffic"; Value = 2},
-        @{Path = "HKLM:\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0"; Name = "AuditReceivingNTLMTraffic"; Value = 2},
-        @{Path = "HKLM:\SYSTEM\CurrentControlSet\Services\Netlogon\Parameters"; Name = "AuditNTLMInDomain"; Value = 2}
+        @{Path = "HKLM:\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0"; Name = "AuditReceivingNTLMTraffic"; Value = 2}
     )
     Set-RegistryConfig -RegPaths $regPaths -Auto:$Auto
 
+    Set-WelaDomainNtlmAudit -Auto:$Auto
+
     # LDAP query logging (Directory Service EventID 1644) - domain controllers only.
     # "15 Field Engineering" = 5 makes expensive / inefficient LDAP searches log as 1644, which surfaces
     # BloodHound / SharpHound-style directory reconnaissance. Only applied where the NTDS role is present.
diff --git a/tests/DomainNtlm.Tests.ps1 b/tests/DomainNtlm.Tests.ps1
new file mode 100644
index 00000000..fb57c41a
--- /dev/null
+++ b/tests/DomainNtlm.Tests.ps1
@@ -0,0 +1,111 @@
+# Safe unit regressions: load function definitions without dispatching WELA or changing host policy.
+$ErrorActionPreference = 'Stop'
+$tokens = $null
+$parseErrors = $null
+$ast = [System.Management.Automation.Language.Parser]::ParseFile((Join-Path $PSScriptRoot '../WELA.ps1'), [ref]$tokens, [ref]$parseErrors)
+if ($parseErrors.Count) { throw ($parseErrors | Out-String) }
+foreach ($functionName in @('Get-WelaDomainNtlmState', 'Set-WelaDomainNtlmAudit')) {
+    $definition = $ast.Find({ param($node) $node -is [System.Management.Automation.Language.FunctionDefinitionAst] -and $node.Name -eq $functionName }, $true)
+    if (-not $definition) { throw "Missing function $functionName" }
+    . ([scriptblock]::Create($definition.Extent.Text))
+}
+function Assert-Equal($Actual, $Expected, [string]$Message) {
+    if ($Actual -cne $Expected) { throw "$Message. Expected '$Expected', got '$Actual'." }
+    $script:assertions++
+}
+function Assert-Throws([scriptblock]$Action, [string]$Message) {
+    $threw = $false
+    try { & $Action } catch { $threw = $true }
+    Assert-Equal $threw $true $Message
+}
+function Reset-Policy($Value, $ProductType = 2) {
+    $script:value = $Value
+    $script:productType = $ProductType
+    $script:writes = 0
+    $script:prompts = 0
+    $script:reads = 0
+    $script:keyExists = $true
+    $script:roleFails = $false
+    $script:readFails = $false
+    $script:writeFails = $false
+    $script:ignoreWrite = $false
+    $script:response = 'Y'
+}
+function Get-CimInstance {
+    param($ClassName, $Property, $ErrorAction)
+    if ($script:roleFails) { throw 'CIM unavailable' }
+    return [pscustomobject]@{ ProductType = $script:productType }
+}
+function Test-Path { param($LiteralPath, $ErrorAction) return $script:keyExists }
+function Get-ItemProperty {
+    param($LiteralPath, $ErrorAction)
+    $script:reads++
+    if ($script:readFails) { throw 'Access denied' }
+    if ($null -eq $script:value) { return [pscustomobject]@{} }
+    return [pscustomobject]@{ AuditNTLMInDomain = $script:value }
+}
+function New-Item { param($Path, [switch]$Force, $ErrorAction) $script:keyExists = $true }
+function Set-ItemProperty {
+    param($LiteralPath, $Name, $Value, $Type, $ErrorAction)
+    if ($script:writeFails) { throw 'Access denied' }
+    if ($Name -ne 'AuditNTLMInDomain') { throw "Unexpected write: $Name" }
+    $script:writes++
+    if (-not $script:ignoreWrite) { $script:value = $Value }
+}
+function Read-Host { param($Prompt) $script:prompts++; return $script:response }
+
+$script:assertions = 0
+foreach ($initial in @($null, 0, 2, 7)) {
+    Reset-Policy $initial
+    Set-WelaDomainNtlmAudit -Auto
+    Assert-Equal $script:value 7 "DC initial value '$initial' reaches Enable all"
+    $expectedWrites = if ($initial -eq 7) { 0 } else { 1 }
+    Assert-Equal $script:writes $expectedWrites 'Already configured DCs are idempotent'
+}
+Reset-Policy 2
+Assert-Equal ((Get-WelaDomainNtlmState).Description) 'Value 2 (not interpreted as Enable all)' 'Migration reports old value without inventing semantics'
+foreach ($role in @(1, 3)) {
+    Reset-Policy 2 $role
+    Set-WelaDomainNtlmAudit -Auto
+    Assert-Equal $script:writes 0 "No domain policy writes on non-DC ProductType $role"
+    Assert-Equal $script:reads 0 'Non-DC domain registry is not read'
+    Assert-Equal ((Get-WelaDomainNtlmState).Description -like 'Not applicable*') $true 'Non-DC is reported as not applicable'
+    Assert-Equal $script:value 2 'Existing non-DC value is preserved'
+}
+foreach ($role in @($null, 0, 42)) {
+    Reset-Policy 2 $role
+    Set-WelaDomainNtlmAudit -Auto
+    Assert-Equal $script:writes 0 'Unknown role never receives domain policy'
+    Assert-Equal ((Get-WelaDomainNtlmState).Description -like 'Unknown*') $true 'Unknown role is not labeled non-DC'
+}
+Reset-Policy 2
+$script:roleFails = $true
+Set-WelaDomainNtlmAudit -Auto
+Assert-Equal $script:writes 0 'Failed role discovery never receives domain policy'
+Assert-Equal ((Get-WelaDomainNtlmState).Description -like 'Unknown*query failed*') $true 'Role errors are visible'
+Reset-Policy 2
+$script:readFails = $true
+Assert-Throws { Set-WelaDomainNtlmAudit -Auto } 'Unreadable DC policy fails visibly'
+Assert-Equal $script:writes 0 'Unreadable current value is preserved'
+Reset-Policy $null
+$script:keyExists = $false
+Set-WelaDomainNtlmAudit -Auto
+Assert-Equal $script:keyExists $true 'Missing DC policy key is created'
+Assert-Equal $script:value 7 'Missing DC key receives Enable all'
+Reset-Policy 2
+Set-WelaDomainNtlmAudit -WhatIf
+Assert-Equal $script:writes 0 'WhatIf preserves policy'
+Assert-Equal $script:prompts 0 'WhatIf does not prompt without Auto'
+$script:response = 'n'
+Set-WelaDomainNtlmAudit
+Assert-Equal $script:writes 0 'Declining preserves policy'
+$script:response = ''
+Set-WelaDomainNtlmAudit
+Assert-Equal $script:value 7 'Confirming applies policy'
+Reset-Policy 2
+$script:writeFails = $true
+Assert-Throws { Set-WelaDomainNtlmAudit -Auto } 'Write failure propagates'
+Reset-Policy 2
+$script:ignoreWrite = $true
+Assert-Throws { Set-WelaDomainNtlmAudit -Auto } 'Read-back mismatch propagates'
+Write-Host "PASS: $script:assertions domain NTLM assertions (mocked; no host changes)."
diff --git a/website/docs/commands/usage.md b/website/docs/commands/usage.md
index 7843242e..5e273ab1 100644
--- a/website/docs/commands/usage.md
+++ b/website/docs/commands/usage.md
@@ -36,6 +36,25 @@ Check the Windows event log file size with Yamato Security's recommendations and
 ## configure
 The `configure` command sets the recommended Windows event log audit policy and file size.
 
+Domain NTLM auditing (`AuditNTLMInDomain`) is set to `7` (**Enable all**) only on
+confirmed domain controllers. Windows clients, member/standalone servers and
+non-DC AD CS servers report **Not applicable** and retain any existing value.
+An unavailable or unknown computer role is reported as **Unknown** and skipped.
+Role detection uses `Win32_OperatingSystem.ProductType=2`, not the presence of
+AD DS tools or a registry key. Before a change, WELA reports the previous numeric
+value; legacy value `2` is not described as full auditing. Changes respect the
+usual confirmation prompt or `-Auto` and are verified by a registry read-back.
+`audit-settings` includes role applicability and the current value in its console
+and CSV output. Incoming and outgoing NTLM controls are separate from this policy.
+
+The [Microsoft NTLM auditing guidance](https://learn.microsoft.com/en-us/defender-for-identity/deploy/configure-windows-event-collection#configure-ntlm-auditing)
+describes the policy and event collection prerequisites. A registry read-back
+does not prove that events were generated, and GPO or MDM may overwrite a local
+change. Validate benign domain NTLM activity and expected Operational events on
+an isolated DC before deployment. `tests/DomainNtlm.Tests.ps1` uses mocked OS and
+registry access; the associated Windows workflow runs Windows PowerShell 5.1 and
+PowerShell 7 without changing host policy.
+
 #### `configure` command examples
 Apply Yamato Security's recommended settings (with confirmation prompt before changing settings):
 ```