diff --git a/ietf/api/serializers_rpc.py b/ietf/api/serializers_rpc.py
index 401cb43a32..0e45ee3b39 100644
--- a/ietf/api/serializers_rpc.py
+++ b/ietf/api/serializers_rpc.py
@@ -571,6 +571,18 @@ class EditableRfcSerializer(serializers.ModelSerializer):
         child=SubseriesNameField(required=False),
         write_only=True,
     )
+    updates = serializers.ListField(
+        child=serializers.IntegerField(),
+        required=False,
+        write_only=True,
+        help_text="List of RFC numbers this document updates."
+    )
+    obsoletes = serializers.ListField(
+        child=serializers.IntegerField(),
+        required=False,
+        write_only=True,
+        help_text="List of RFC numbers this document obsoletes."
+    )
 
     class Meta:
         model = Document
@@ -584,8 +596,28 @@ class Meta:
             "std_level",
             "subseries",
             "keywords",
+            "updates",
+            "obsoletes",
         ]
 
+    def _validate_rfc_number_list(self, field_name, rfc_numbers):
+        """Raise ValidationError if any RFC numbers in the list don't exist."""
+        unknown = [
+            n for n in rfc_numbers
+            if not Document.objects.filter(rfc_number=n, type_id="rfc").exists()
+        ]
+        if unknown:
+            raise serializers.ValidationError(
+                {field_name: [f"Unknown RFC number: {n}" for n in unknown]}
+            )
+        return rfc_numbers
+
+    def validate_updates(self, value):
+        return self._validate_rfc_number_list("updates", value)
+
+    def validate_obsoletes(self, value):
+        return self._validate_rfc_number_list("obsoletes", value)
+
     def create(self, validated_data):
         raise RuntimeError("Cannot create with this serializer")
 
@@ -602,6 +634,8 @@ def update(self, instance, validated_data):
         published = validated_data.pop("published", omitted)
         subseries = validated_data.pop("subseries", omitted)
         authors_data = validated_data.pop("rfcauthor_set", omitted)
+        updates = validated_data.pop("updates", omitted)
+        obsoletes = validated_data.pop("obsoletes", omitted)
 
         # Transaction to clean up if something fails
         with transaction.atomic():
@@ -673,6 +707,24 @@ def update(self, instance, validated_data):
                                 )
                             )
                         )
+            if updates is not omitted:
+                RelatedDocument.objects.filter(
+                    source=rfc, relationship_id="updates"
+                ).exclude(target__rfc_number__in=updates).delete()
+                for rfc_num in updates:
+                    target = Document.objects.get(rfc_number=rfc_num, type_id="rfc")
+                    RelatedDocument.objects.get_or_create(
+                        source=rfc, relationship_id="updates", target=target
+                    )
+            if obsoletes is not omitted:
+                RelatedDocument.objects.filter(
+                    source=rfc, relationship_id="obs"
+                ).exclude(target__rfc_number__in=obsoletes).delete()
+                for rfc_num in obsoletes:
+                    target = Document.objects.get(rfc_number=rfc_num, type_id="rfc")
+                    RelatedDocument.objects.get_or_create(
+                        source=rfc, relationship_id="obs", target=target
+                    )
 
             # update subseries relations
             if subseries is not omitted:
diff --git a/ietf/api/tests_serializers_rpc.py b/ietf/api/tests_serializers_rpc.py
index 167ffcd3ee..5151f337d5 100644
--- a/ietf/api/tests_serializers_rpc.py
+++ b/ietf/api/tests_serializers_rpc.py
@@ -215,3 +215,27 @@ def test_partial_update(self, mock_trigger_red_task, mock_update_searchindex_tas
             mock_update_searchindex_task.delay.call_args,
             mock.call(rfc.rfc_number),
         )
+
+    def test_unknown_rfc_number_rejected(self):
+        """Unknown RFC numbers in updates/obsoletes should cause validation failure."""
+        from django.db.models import Max
+
+        rfc = WgRfcFactory()
+        unknown_rfc_number = (
+            Document.objects.filter(rfc_number__isnull=False).aggregate(
+                m=Max("rfc_number") + 1
+            )["m"]
+            or 10000
+        )
+
+        for field in ("updates", "obsoletes"):
+            serializer = EditableRfcSerializer(
+                partial=True,
+                instance=rfc,
+                data={field: [unknown_rfc_number]},
+            )
+            self.assertFalse(
+                serializer.is_valid(),
+                msg=f"{field} with unknown RFC number should be invalid",
+            )
+            self.assertIn(field, serializer.errors)