"Xiang-yu" or the Ayu (Plecoglossus altivelis T. et S.) is one of the deliciousfood fishes. The present paper deals with the results on observation of the its reproduc-tive biology in Fuxi Stream, Zhejiang, during the years from 1979 to 1980. The results are summarized as follows: All individuals of one year old attain sexual maturity. The developmental processesof the gonads are quick. The ovary develops to stage Ⅱ in July, and attains to stageⅣ till middle September. The absolute fecundity varies with body length as wellas body weight, ranging from 10,659 to 65,156 eggs, average 30, 135. The relativefecundity is on an average of 730. 26. per gram. In the early September the adult fishes begin to migrate to the spawning ground.The breeding season of the Ayu in Fuxi Stream is from October to December, butthe main Spawning activity takes place between middle October to early November.The time of spawning prevails usually from sunset to early morningat about 6 a. m. The spawning grounds is situated at the brackish water region where the depth ofwater varies from 25 to 35 cm, with gravel and sand bottom and running water. Thewater-temperature is about 21-14μ, and the salinity varies from 0.5 to 8.5‰. Theeggs are adhesive and sink down to the bottom. Each female fish released eggs two or three times in a breeding season. Afterspawning most of the parents died.