According to age and sex,32 rats and 32 mice were divided into 8 groups. The activities of mATPase of soleus muscle were detected by the mATPase method. Then the percentage of type Ⅰ and Ⅱ fibres were determined. The viscera weight and viscera index were measured and calculated. The result revealed: As far as the proportion of type Ⅱ fibres in soleus was concerned,①the youngs was notably higher than that of the adult in both rat and mouse;the female adults was lower than that of in male adult;②the adult rats was markedly lower than that of in adult mouse. The thymus indexes and the splenic indexes (SI) in young rat and mouse were both markedly higher than that of in adult,whereas the hepatic indexes (HI) were both distinctly lower than that of in adult. The HI and the SI in young and adult rat were prominently lower than those of the corresponding group of mouse. The above results suggested that the activities of mATPase declined during development both in rat and mouse. So the proportion of type Ⅱ fibres gradually decreased. And the activities of mATPase show obvious sex disparities and interspecific diversity.