Comparative studies on the uptake and elimination of radionuclides, 6OCo, 131I, 137Cs, 144Ce and 106Ru by the advanced fry and the fingerlings of rainbow trout were conducted under laboratory conditions. The general patterns of uptake of 60Co, 131I, 144Ce, 106RuNO-nitro and -binuclear complexes by both the advanced fry and the fingerlings were similar to each other. On the other hand, the uptake of 137Cs by the advanced fry was more rapid than that by the fingerlings although the uptake of 106RuNO-nitrato complex by the advanced fry was much slower. The remarkable differences in rate of uptake and turnover rate for 137Cs and in turnover rate for 144Ce were observed between the advanced fry and the fingerlings. The concentration factors for 60Co and 137Cs in the fry increased with growth of the fish. However, this trend was not necessarily observed for 131I, 144Ce and 106RuNO complexes. In comparison of the tissue uptake of the radionuclides, the high concentration factor for 60Co, 106RuNO complexes and 141Ce in viscera including digestive tract were observed, while for 131I in the gills.