Abstract: By electron microscopy, spermathecal ultrastructure of the freshwater crab Sinopotamon yangtsekiense was studied for the first time. The results showed that there were vast arrays of cisternaes and vesicles of rough endoplasmic reticulum and Golgi complexes containing flocculent and granular secretions in the topcrine gland cells. At first the cisternaes and vesicles were separated, then they began to aggregate in masses forming bigger granules and excluded from spermathecal epithelium.Ribosome is widely distributed. Mitochondria were numerous and functional in secretion. Cytochemistry revealed that the secretions were consisted of proteins, lipids and carbohydrate.