This study, taken by the light and the electron microscopy, shows that each gill of Eriocheir Sinensisl has an axis and two series of lamellae running in parallel on both sides.The gill is composed of corneum, epithelial cells, and basement membrane.The epithelial cells enlarge the surface by protruding digital mucrones-Some epithelial cells stand out to wards the gill cavity and form the septum in it.The big cells in the gill cavity are developed from epithelial cells, wThidi protrude into the gill cavity and grow bigger and bigger, finally into big cells.Big cells separate tne gill cavity into many circuitous channels, which makes it easier to exchange gas and the absorb substance.