Abstract: 10-day old Muscovy ducks were infected with Muscovy Duck Reovirus. Apoptosis were detected and the expression of FasL were studied in many infected tissues post infection, using in-situ end labeling technique and immunohisto chemistry method. The result of in-situ end labeling revealed that a large number of positive cells were found in many tissues， which showed that Muscovy duck reovirus could induce varying-degreed apoptosis in the liver，spleen，kidney，lung，thymus，cecum and bursa of fabricius. The result of immunohistochemical study showed that the expression of FasL were observed in liver, kidney, lung，thymus，cecum and bursa of fabricius，and the changes of FasL expression were highly correlated with the level of apoptotic index. The results showed that the mechanism of apoptosis induced by Muscovy duck reovirus is closely related with the expression of FasL.