diff --git a/OpenAPI/TS28541_NrNrm.yaml b/OpenAPI/TS28541_NrNrm.yaml
index 8c7a4a8a89a491bb64fc60cc62ec9c9bc1bc9470..b58a1a12f55c82bfb53bad8688c6e57922e537c5 100755
--- a/OpenAPI/TS28541_NrNrm.yaml
+++ b/OpenAPI/TS28541_NrNrm.yaml
@@ -43,6 +43,7 @@ components:
           $ref: '#/components/schemas/Sst'
         sd:
           type: string
+          pattern: '^[A-Fa-f0-9]{6}$'
 
     PlmnIdList:
       type: array