Fragmentations of different rigor type muscles during postmortem storage were studied and glycerinated muscle fibers were employed in order to determine the factors influencing fragmentation. Degree of fragmentation was significantly different on different rigor types. Fragmentation of acid rigor proceed rapidly during postmortem aging while it was very slow in alkaline rigor. Similar results were obtained when glycerinated muscle fibers were incubated with sarcoplasm extracted from two types of rigor muscle. The protein compositions of sarcoplasm from two rigor types were not significantly different. But the fragmentation of the two rigor types changed according to the pH change. The same effects were also obtained by use of Ca^(2+) Under the conditions of acid rigor sarcoplasm, fragmentation was not suppressed by the addition of the lodoacetate, irreversible inhibitor of CAF. On the other hand, the fragmentation was not increased by the addition of Ca^(2+) alone under conditions alkaline rigor sarcoplasm. From these results it can be suggested that the fragmentation of different rigor types are influenced by different factors and Ca^(2+), CAF and proteases are involved with a complex relationship.