Population of Ayu-fish in the lower reaches of the Yodo River System owes to the number of young fish migrating up-stream from the Osaka Bay in spring to early summer every year. Variations in the total number of upstream migration have been attributed to coastal environmental factors affecting survival ratio of the juvenile fish. In order to predict the number of their upstream migration in the Yodo River, we made correlation and regression analyses between the annual total number of upstream migration and a set of coastal environmental factors in the previous autumn to winter season in the Osaka Bay. Results indicated that cold water temperature less than 9℃ in winter and Chl.a concentration in autumn in the Osaka Bay were positively correlated with the upstream migration of Ayu-fish to the Yodo River.