Abstract: Praziquantel is a new chemotherapeutic agent against schistosomiasis and cestodiasiswith remarkable efficacy and low toxicity. In this paper, Praziquantel was used in the treatment of experimental infection of clonorchiasis and paragoniamiasis in rats and dogs.In the case of clonorchiasis, the worm reduction rate was 95～97% in rats treated with the total dose of 300 mg/kg when the animals were sacrificed 15 days after the completion of treatment. The worm death rate was 93% in the dog examined 48 hours after treatment with a single dose of 75 mg/kg.In the case of paragonimiasis, the worm death rate was 87% in the dog treated with the total dose of 100 mg/kg and examined 48 hours after treatment. The worm death rates were only 37% and 24% when 75 mg/kg and 50 mg/kg were given respectively.It is concluded that Praziquantel is a promising new drug in the treatment of human clonorchiasis and paragonimiasis, although the optimal dosage schedule awaits elucidation.