Abstract: Comparative sperm morphology of three species of crab,Portunus trituberculatus,Eriocheir sinensis and Sinopotamon yangtsekiense have been investigated with light and electron microscopes.These sperms are aflagellate and typical brachyurans.SEM observation shows:1)each sperm has a spherical body,2)the anterion part appears smooth,and the other part is uneven,from which 10-20 radial arms radiate,3)there is a ditch ring between the two parts.TEM reveals that each sperm is composed of acrosome,cytoplasmic region,nuclear cup and radial arms.The globular acrosome is a very complicated structure and shows PAS positive.Its centre is a cylindrical acrosomal tubule and its front is an apical cap.The acrosome is limited by an single continuous membrane and surrounded by nuclear cup,which shows Feulgen positive.The nuclear cup contains uncondensed chromatin and is bounded by a complete nuclear envelope.The radial arms are extensions of the nuclear cup.They are stational,then the sperm are immotile.There are no microtubular elements in the arm.The cytoplasmic region is posterior to the acrosome and consists of lamellar complex.Several differences exist the crab spermatozoa in three species.