Objective: To investigate the mutation and its treatment measures in a paternity case detecting short tandem repeat (STR) loci by the IdentifilerTM system.Method: Extracting genomic DNA from blood samples and detecting 36 STR loci with the IdentifilerTM and AGCU21+1STR labeling kit.Results: In IdentifilerTM detection system, one step mutation of D2S1338 locus was found.The detection results of other loci were consistent with the genetic law.Conclusion: The 20 non-CODIS STR loci of AGCU21+1 system can be used as a complementary test genetic markers to deal with the mutation in paternity.