This study was undertaken to investigate the effects of age and of the dietary protein sources & levels on urinary calcium excretion and bone metabolism in the rats. Two experiments were conducted . In experiment U, 6& 20 weeks old rats were fed 8 & 36%, casein & ffish protein diet for 5 weeks . In experiment II, 16& 52 weeks old rats were fed 40 % protein diets, protein sources were casein, fish and gluten. High-protein diet group excreted more caldium in urine than low-protein group. Urinary calcium excretion was affected by the sources of protein ; gluten group excreted more Ca, followed by fish & casein group. Total bone Ca & Ca proportion in ash were higher in 20 weeks old rats than 6 weeks old rats, but 16 & 52 weeks old rats showed no differences. bone composition showed that water proportion was high and ash proportion was low in 6 weeks old rats than in 20 weeks old rats. However, these tendencies were not observed between 16 weeks and 52 weeks old rats. And bone composition was affected by protein sources ; higher ash proportions were noted in one order of casein, fish, and gluten water proportion were lower in one same order.