Abstract: Effect of oral administration of single subcurative dose (300 mg/kg) of pyquiton (praziquantel) on the tegumental surface of adult schistosoma japonicum were studied using scanning electron microscope. Bisexual worms were perfused out from the liver of infected mice between 10 minutes and 48 hours after medication. Tegumental surface alternations were observed and became rather apparent 1～2 hours after medication. Major surface alterations included pronounced swelling, wrinkling, tough junction and fusion of ridges, emergence of numerous ball-like materials of bulbs on the ridges. enlargement and collapse of sensory structures, erosion and peeling of the tegumental surface, and attachment of the host leukocytes to denuded surface.