diff --git a/OpenAPI/TS28541_NrNrm.yaml b/OpenAPI/TS28541_NrNrm.yaml
index 1dbce0d987164e7d31edb65461b19925ee4a82a3..5edb3c0c6ab72bc442f4a9f24729fb1b5f446868 100644
--- 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