Abstract: To detect the liver spontaneous lesions of beagle dogs used in toxicity studies. Sixty beagle dogs from control experimental groups, age from 10-18 months were used. Liver fune-tion index of serum were tested and liver samples were observed by routine histological tech-nique. The results revealed that all 7 clinical index were deviated in different degree.Various spontaneous lesions amounting to 20 kinds in different degrees were found in 63.3% dogs of the study,including hepatocyte degenerations,necroses,and proliferations,connective fiber prolifer-ations and fibrosis,inflammatory cell infiltration,abscess and cystis. The degree and the frequen-cy of levsions was no difference between the sex. Usually several kinds of lesions occurred in the liver of one dog. It is suggested that spontaneous lesions should be monitored so as to provide histopathological investigations for safety estimation experiment of new medicine.