diff --git a/libraries/pbsExtensions/processors/adUnitCode.js b/libraries/pbsExtensions/processors/adUnitCode.js
new file mode 100644
index 00000000000..f936e0f662f
--- /dev/null
+++ b/libraries/pbsExtensions/processors/adUnitCode.js
@@ -0,0 +1,13 @@
+import {deepSetValue} from '../../../src/utils.js';
+
+export function setImpAdUnitCode(imp, bidRequest) {
+  const adUnitCode = bidRequest.adUnitCode;
+
+  if (adUnitCode) {
+    deepSetValue(
+      imp,
+      `ext.prebid.adunitcode`,
+      adUnitCode
+    );
+  }
+}
diff --git a/libraries/pbsExtensions/processors/pbs.js b/libraries/pbsExtensions/processors/pbs.js
index 56a2a391c76..0ed2d12fad8 100644
--- a/libraries/pbsExtensions/processors/pbs.js
+++ b/libraries/pbsExtensions/processors/pbs.js
@@ -3,6 +3,7 @@ import {deepAccess, isPlainObject, isStr, mergeDeep} from '../../../src/utils.js
 import {extPrebidMediaType} from './mediaType.js';
 import {setRequestExtPrebidAliases} from './aliases.js';
 import {setImpBidParams} from './params.js';
+import {setImpAdUnitCode} from './adUnitCode.js';
 import {setRequestExtPrebid, setRequestExtPrebidChannel} from './requestExtPrebid.js';
 import {setBidResponseVideoCache} from './video.js';
 
@@ -26,6 +27,10 @@ export const PBS_PROCESSORS = {
       // sets bid ext.prebid.bidder.[bidderCode] with bidRequest.params, passed through transformBidParams if necessary
       fn: setImpBidParams
     },
+    adUnitCode: {
+      // sets bid ext.prebid.adunitcode
+      fn: setImpAdUnitCode
+    }
   },
   [BID_RESPONSE]: {
     mediaType: {
diff --git a/modules/prebidServerBidAdapter/ortbConverter.js b/modules/prebidServerBidAdapter/ortbConverter.js
index 0aee261c25d..83335f81bc2 100644
--- a/modules/prebidServerBidAdapter/ortbConverter.js
+++ b/modules/prebidServerBidAdapter/ortbConverter.js
@@ -246,6 +246,7 @@ export function buildPBSRequest(s2sBidRequest, bidderRequests, adUnits, requeste
     impIds.add(impId)
     proxyBidRequests.push({
       ...adUnit,
+      adUnitCode: adUnit.code,
       ...getDefinedParams(actualBidRequests.values().next().value || {}, ['userId', 'userIdAsEids', 'schain']),
       pbsData: {impId, actualBidRequests, adUnit}
     });
diff --git a/test/spec/ortbConverter/pbsExtensions/adUnitCode_spec.js b/test/spec/ortbConverter/pbsExtensions/adUnitCode_spec.js
new file mode 100644
index 00000000000..e17f9e856b0
--- /dev/null
+++ b/test/spec/ortbConverter/pbsExtensions/adUnitCode_spec.js
@@ -0,0 +1,23 @@
+import {setImpAdUnitCode} from '../../../../libraries/pbsExtensions/processors/adUnitCode.js';
+
+describe('pbjs -> ortb adunit code to imp[].ext.prebid.adunitcode', () => {
+  function setImp(bidRequest) {
+    const imp = {};
+    setImpAdUnitCode(imp, bidRequest);
+    return imp;
+  }
+
+  it('it sets adunitcode in ext.prebid.adunitcode when adUnitCode is present', () => {
+    expect(setImp({bidder: 'mockBidder', adUnitCode: 'mockAdUnit'})).to.eql({
+      'ext': {
+        'prebid': {
+          'adunitcode': 'mockAdUnit'
+        }
+      }
+    })
+  });
+
+  it('does not set adunitcode in ext.prebid.adunitcode if adUnit is undefined', () => {
+    expect(setImp({bidder: 'mockBidder'})).to.eql({});
+  });
+});