Abstract: The morphological variation of nucleus during spermatogenesis in Macrobrachium nipponense and its status during the reproductive evolution of Caridean shrimp were investigated using transmission electron microscopy(TEM) technique. During the whole process of spermatogenesis, the nuclear morphology of spermatogenic cell varied from spherical or ellipsoidal to shallow-dish-like shape,and the nuclear membrane existed only in the rear part of mature sperm varied from intact to unintegrated one. The chromatin gradually varied from loosen to coacervative one, and then,developed differentially into two types of nucleus in the mature sperm,i.e.,vesicular nucleus and filamental nucleus, which became an important characteristics of Macrobrachium nipponense.These nuclear morphological variations could be regarded as an important classifying property among Decapoda, on which,studies could contribute much to the analysis of the status of this species in the reproductive evolution of Caridean shrimp.