Abstract: This paper deals with the ultrastructural study of the spermatogenesis and sustentacular cell of the testes of Schistosoma japonicum by means of TEM. Albeit several papers have reported on the ultrastructural studies of the testes of male reproductive organ of S. mansoni, no systemic observation on the spermatogenesis of schistosome and ultrastructure of the testes of 5. japonicum was available .The authors described the characteristics of the spermatogonium, spermatocyte and different appearance of spermatids. The latter was subdivided into 4 types, namely, Sda, Sdb, Sdc and Sdd, which could be identified by the features of nuclear shape and the density of matrix, the distribution of the mitochondria in the cytoplasm, the appearing and the formation of the acrosome-like structure, the presentation and elimination of the residual bodies, etc. The spermatids were embedded and interdigitated among the sustentacular cells, forming a complicated picture in the field of TEM. The acrosome-like structure and the inclusion of residual bodies were revealed in developing spermatids. The origin and the characteristics of these structures were discussed.