Some effect on the protein metabolism in growing albino rats by feeding on the rice mixed with wheat or barley have been studied. The species of wheat and barley used in this experiment were either 80% polished or nonpolished wheat, barley and naked barley. The growing rats to be examined were fed on 30% wheat or barley mixed with rice diets for 8 weeks. The total nitrogen, creatinine, amino acid nitrogen and urea-nitrogen contents in the liver and the creatinine and urea-nitrogen contents in the urine have been measured. The results obtained are summarized as follows: 1. The total nitrogen contents in the liver and the serum were no remarkable difference by feeding on each mixed diet, compared with the rice diet group. 2. The creatinine contents in the liver of the unpolished wheat and barley mixed diet groups were the similar to that of the rice diet group, but these were higher by feeding on the polished wheat and barley mixed with rice diets. 3. The amino acid nitrogen contents in the liver of the polished naked barley mixed with rice diet groups were the similar to that of the rice diet group, but these were higher by feeding on the other mixed diets than the rice diet. 4. The urea-nitrogen contents in the serum of the polished wheat and naked barley mixed with rice diet groups were higher than that of the rice diet group, but these were significantly lower by feeding on the polished barley mixed with rice diets than the others. 5. The creatinine and the urea-nitrogen contents in the urine of the original wheat and barley mixed with rice diet groups were higher than that of the polished wheat and barley mixed with rice diet groups. In the view of the above results, it could be seen that the protein metabolism was remarkable change according to polish of the wheat and barley.