A histological study on the development of the ovary of Ayu, Plecoglossus altivelis was carried out through the years from 1979 to 1980. All the fish were sampled fromthe river "Wu Qi" in Zhejiang province. From December to April, the gonad has not yet differentiated; duringMay to August the ovary enters into stage Ⅱ; From early September to middle Sep-tember, the ovary develops into stage Ⅲ; from middle september to early October itenters stage Ⅳ. The spawning season of Ayu is in October-November the ovaryreached to stage Ⅴ, and the oocytes is mainly in phase 5, but also contains the phase4,3,2 and 1. After the releasing of one bateh of eggs, the spent ovary is observed tobe in state Ⅵ-Ⅳ, the oocytes are mainly in phase 4 and empty follicles, then theovary develops again into stage Ⅴ' and the next spawning takes place. The ovarydevelops to stage Ⅴ once again. Evidently the development of the oocytes in the ovaryof Ayu is in successive processes and the female releases eggs 3-4 times in onespawning season. In the stage Ⅱ of the development of oocytes, the nucleolus containing substancewhich is possibly related to the fomation of yolk within the oocyte, enters into cyto-palsm by the part rupture of the nuclear membrane. In the middle stage of phase 2, there is a transparent layer surrounding thenucleus. Egg membrane of Ayu is composed of 3 layers: plasma membrane, zona radiataand attachment membrane which is present in the oocyte in phase 3. A syncytium is conical in shape and located near the fertilization orifice consistingof more than 10 cells.