Abstract: From September to November in 1994, the freshwater crab Sinopotamon yangtsekiense collected from Anhui Province were observed in detail with transmissionelectron microscope (TEM) and cytochemical methods. The early spermatid is smallwith an oval shaped nucleus. The spermahd began to differentiate, and changed intolonger elliptical shape, nuclear-plasm redistributed and moved towards two ends of thecell. The acrosome of sperm derived from Golgi body. The vesicles which producedfrom Golgi body aggregated to form a large proacrosomal vesicle. The proacrosomalvesicle further develop into acrosomal vesicle. The nuclear membrare changes into acup-like shape and surrounds the acrosomal vesicle, between the two parts, and thena layer of membrane complex appears. The nuclear cup was positive and acrosomePAS positive.