Abstract: OBJECTIVE To detect and compare the toxicity action of Azidothymidine myristate liposome (AZT-ML) and Azidothymidine(AZT) in Kunming mice and Beagle dogs. METHODS Detecting acute LD50 of two drugs by tail interavenous injection in mice. The mice were divided into 3 groups to observe the effect of action, body weight and organ coefficient. Another, the dogs were divided into 3 groups to observe the effect of action, body weight, organ coefficient, blood physiological index, serum biochemical parameters and organ pathology. RESULTS LD50 of AZT was 12.50 mg·kg-1, LD50 of AZT-ML was 20.30 mg·kg-1. Action of mice was normal, the change of body weight, organ coefficient of mice, AZT-ML group had significant decreases by comparing with AZT group. Action of dogs was normal, the change of action, body weight, organ coefficient, blood physiological index, serum biochemical parameters and organ pathology of dogs, AZT-ML group had significant decreases by comparing with AZT group. CONCLUSION To compare with AZT, AZT-ML can significantly reduce impairment of organism and toxicity of laboratorial animal.