Abstract: Praziquantel, administered orally to mice at a single dose of 200～600 mg/kg 2 h before inoculation, exhibited a protective effect against Schistosoma japonicum cercariae infection. Part or most of the schistosomules recovered from the skin of mice which were inoculated with cercariae for 15 min to 2 h were dead. On the other hand, an apparent decrease of cercariae penetrating the isolated skin of mice treated orally with praziquantel 2 h before was observed. Further studies indicated that in dechlorinated water cercariae were more sensitive to praziquantel than those in Hanks' balanced salt solution. Since praziquantel can be excreted and secreted from the skin of mouse treated with the drug orally, the cercariae could be succumbed by praziquantel on the surface of the skin.