The present paper describes the ultrastructure of the surface topography, head organ, tegument, musculature, glandular system, primary alimentary tract and flame cells of the Chinese mainland strain of Schistosoma japonicum cercaria, as visualized with both scanning and transmission electron microscopes. The results not only illustrate the morphological features of the cercarial surface and its internal structure reflecting an adaptation to the aqueous habitat but also reveal the correlation between the morphological structure and physiological function.