The effect of zinc on bone metabolism was investigated in weanling rats orally administered zinc sulfate (0.1, 1.0 and 10 mg Zn/100g body wt) for 30 d. The administration of zinc produced dose-dependent increases in zinc contents of the femoral diaphysis and epiphysis. The dry weight of the femur was significantly increased by the doses of 0.1 and 1.0 mg Zn/100 g for 3d, while significant reduction of that was observed by zinc administration for 30 d. Meanwhile, DNA content, calcium content and alkaline phosphatase activity in the femoral diaphysis and epiphysis were significantly increased by the doses of 0.1 and 1.0 mg Zn/100 g for 3 d. However, by the 30 d administration of zinc (0.1, 1.0 and 10 mg/100 g), calcium contents in the femur and serum were markedly decreased. These results suggest that comparatively low dose of zinc may stimulate the bone growth and calcification of weanling rats.