It is difficult to mechanical classification of seafood. Especially shellfish, more difficult to check for quality evaluation. Also, particular shell that korean usually eat did not listed on quality certification. This paper focus on the sound that is new method of finding out faulty shell while rolling on flat rock. We suppose there is an obvious contrast between normal and faulty Ruditapes philippinarum. and we analysis rolling sound of four group; Group A(4 normal Ruditapes philippinarum), Group B( 3 normal +1 faulty ), Group C (2 normal +2 faulty), Group D(1 normal +3 faulty). As a result, We found that Group A had higher rate in low frequency than other groups. Hunman were difficult to recognize this different but, we hope that it would be helpful for shellfish classification systems.