Abstract: The morphology and ultrastructure of the sperm of the freshwater shrimp,Macrobrachium nipponense, were studied with electron microscopy and cytochemical cytochemical methods.The results show that the nonflagellated, nonmotile sperm resembles everted umbrella and is composed of spike-anterior in position, cap -shaped part at the middle and main-body part at the rear which contains a nucleus.The nucleus is decondensed and contains many flocculent materials.The nucleus is not delimited by a nuclear membrane and shows feulgen positive.The cytoplasm of the cap-shaped part contains a pair of centrioles which is composed of nine doublet tubules and 15-20 radial fibrils which anastomose to form the spike.Both the spike and the radial fibrils are cross-striated with a periodicity of 35 nm. These structures contain 4-7 nm filaments running perpendicularly to the cross striation. No clearly definable acrosomal region is identifiable morphologically.