To investigate the quality changes during frozen storage, top shell, Omphalius pfeifferi capenteri, was stored at -18$^{circ}C$, -$25^{circ}C$ and -3$0^{circ}C$ immediately after shelling and water holding capacity, protein composition and histological features were examined with the lapsed period of the storage. During the storage period, amount of free drip was increased with higher frozen temperature and longer frozen period, but with the longer storage period, the lower water holding capacity was observed. The extractability and composition of muscle protein, sarcoplasmic protein and stroma protein were rather stable regardless of frozen temperature and frozen storage period. However, the extractability of myofibrillar protein was decreased with higher frozen temperature and longer frozen storage period. On the changes of muscle tissue structure, following points were observed. 1) In the muscle tissue structure of fresh sample, fine muscle fiber was closely distributed all over the tissue regardless of cross and longitudinal section. 2) In tissue structure under frozen state, it was observed that ice crystals apparently grew with the higher storage temperature. Empty spaces between muscle bundles which wee formed by aggregations of muscle fiber were observed after 3 months storage at -18$^{circ}C$ . 3) Tissue structure in thawed state was restored satisfactorily after 1 month storage regardless of storage temperature. After 3 months storage at -3$0^{circ}C$, muscle tissue was well restored, but at -18$^{circ}C$, empty spaces were apparent due to incomplete restoration.