Summary: In order to study the expression of IL-1β and TNF-α in the myocardium of MCMV myocarditis and their role in the myocardial damages, 60 BALB/C mice of 4 weeks were randomly divided into two groups: 36 were injected intraperitoneally with MCMV and 24 served as control group. Immunohistochemistry was used to detect IL-1β and TNF-α expression in the myocardium, and myocardial lesions were observed histopathologically. Histopathological study on the myocardium from infected mice revealed focal or diffuse lesions characterized by inflammatory cells and degeneration or necrosis of myocytes. The myocardial lesion score showed the degree of inflammatory cell infiltration was slight in MCMV myocarditis.The positive staining signals for IL-1β and TNF-α proteins which mainly located in the infiltrating inflammatory cells and degenerative or necrotic myocytes were markedly detectable whereas there were no positive findings in the myocardium of control mice. IL-1β and TNF-α was expressed in the myocardium of viral myocarditis murine model induced by MCMV. IL-1β and TNF-α may play an important role in the pathogenesis of viral myocarditis.