AIM:To demonstrate the inhibitoary effects of Longkai Granules(LKG) against experimental prostatic hyperplasia and evaluate its toxicity on animals taking the granules orally. METHODS: The prostate exponent,DNA content in prostate tissue、the activity of acid phosphatase in serum or the wet weight of spermatophores and testicles in normal immature mice and in the hyperplasia model mice induced by subcutaneous injecting testooslerone spropionate or by implanting of the urogenital sinus were determined after administrating of LKG intragastrically to the mice.The single maximum dosage of LKG in mice and its long-term(13 weeks) toxicity in Wistar rats and Beagle dogs in orally was evaluated. RESULTS: LKG could decrease the weights of prostates and DNA content in the tissue in the normal immature mice in the amount of 20 and 40 g/kg once a day.LKG,in the amount of both 10,20 and 40 g/kg for 10 days and 20 and 40 g/kg for 30 days,could inhibit the hyperplasia of ventral prostates in the model mice induced respectively by the injection of testooslerone spropionate and by implanting urogenital sinus.LKG,in the(amount) of 100 g/kg for 13 weeks to Wistar rats,would lead to prostatic atraphy in alight degree,and its epithelial cells change in shape from column to flat and prostatic cavity being small,which did not recover in 4 weeks after stopping administration of tested drug to the animals.The single maximum dosage by ig in mice was 200 g/kg.There was no significant toxicity reaction in rats in the amount of 10,40 and 100 g/kg for 13 weeks or in Beagle dogs in the amount of 12 and 60 g/kg for 13 weeks. CONCLUSION: LKG can inhibit the prostatic hyperplasia and shows no visible toxic reaction in animals orally.