Objective To observe the influence of testosterone deficiency on pathological changes of liver, skeletal muscle and pancreatic islet of male rats. Methods Healthy male SD rats were randomly assigned into normal control group (n=5, sham castration was performed), castrated group (n=7, testosterone deficiency model was established with castration) and replacement group (n=5, castration was performed, and intraperitoneal injection of 12.5 mg/kg testosterone propionate was conducted for 10 weeks). Thirty weeks later, serum concentration of testosterone was measured by radioimmunoassay in each group. The tissues of liver, skeletal muscle and pancreatic islet were obtained, and were observed by light microscopy with HE staining. Results The serum concentration of testosterone in castrated group was significantly lower than those in normal control group and replacement group(P<0.01). Light microscopy revealed that there was accumulation of lipid droplets in the cytoplasm of liver in castrated group, and there were less lipid droplets in replacement group than in castrated group. The size of nuclei in castrated group was smaller than that in normal control group. In castrated group, most skeletal muscle tissues were not clear in cross-sectional diameter, the pattern of cross striation in muscles disappeared, swelled and arranged in disorder, and the round lipid droplets were seen focally. However, the structure of muscle tissues in replacement group was similar with that in normal control group. The histological structure of pancreatic islet β cells was normal in normal control group, and the histological structure in castrated group and replacement group was similar with that in normal control group. Conclusion Fat deposition may cause pathological damage to liver and muscle tissues of male rats with castration, and exogenous testosterone replacement therapy may improve the pathological changes to some degree.