Abstract: Mice harbouring different developmental stages of Schistosoma japonicum were treated orally with praziquantel at a single dose of 400 mg/kg and sacrificed 0.5-24 h after the medication for histological observation.After praziquantel treatment, the tegument of dc(3 h), d28, d35, and d42 schistosomes showed extensive vacuolation and rupture, while in d3, d7, d11, d14 and d21 schistosomules, little or only a mild local vacuolation of the tegument was detected. Strong host celt response was seen around the damaged d0, d28, d35 and d42 schistosomes, and the cells found were largely polymorphonuclear leucocytes. However, around d3-21 schistosomules, the cells were mainly lymphocytes and the host cell response was rather weak.The results confirmed that Schistosoma japonicum exhibited stage-specific susceptibility to praziquantel.