The structural change of the oviduct of freshwater shrimp (Macrobrachium nipponense) during spawning was examined by electron microscopy. The oviduct wall structural characteristics seem to be influenced significantly by the spawning process. Before the parturition and ovulation, two types of epithelial cells (types Ⅰ and Ⅱ) are found in the epithelium. The free surfaces of type Ⅰ and type Ⅱ cells have very dense long microvilli. Under the type Ⅰ and type Ⅱ cells, are a relatively thick layer of secreting material and a layer of mostly dead cells. After ovulation, two other types of epithelial cells (types Ⅲ and Ⅳ) are found in the oviduct wall epithelium. The free surface of type Ⅲ cells only has short microvilli scattered on the surface. The thick layer with secreting material and the dead cell layer disappeared at this stage. In some type Ⅲ cells, the leaking out of cytoplasm from broken cell membrane led to the death of these type Ⅲ cells. The transformation of all four types of epithelial cells was in the order:Ⅳ→Ⅰ→Ⅱ→Ⅲ.