Ultrastructure of spermatozoa of E. septemfasciatus was investigated using transmission electron microscopes. The spermatozoa consists of two parts: the head and the tail (flagellum), no midpiece. The spermatozoa of E. septemfasciatus has no acrosome. A large spherical nucleus, covered with nuclear membrane, is located at the front part of the head and about its 1/3. The high electron density chromatin is the main components of nucleus, with several low electron density vesicles in it. There is little space between the plasma membrane and nuclear membrane at the front part of head. The implantation fossa is located in the posterior end of the nucleus. Proximal centriole and intercentriolar body are located in implantation fossa. The posterior end of the head is a large sleeve, which is about 2/3 of the head. The sleeve contains centriolar complex, several mitochondria and vesicles. At the midpart of the sleeve, there is a sleeve carve, out of which the thin and long tail stretches. The tail with only a little cytoplasm is thin and long. The axoneme between the end of the base body and the head of the tail is “9+0”. The 9 doublet of the axoneme, the central structure of the tail, is connected to the 9 strips of the posterior end of the basal body. The flagellar tail is the conventional “9+2”axoneme.