The male rats after weaning were fed with the mixed diets of rice and some cereals for three weeks in a ad-libitum method. The growthgain of rats were determined by feeding those diets and the contents of free basic amino acids level in plasma were analyzed by amino acid analyzer. The results were as follows; 1. Rice diets group was highest in growthgain and weightgain, the second was the mixed of 80% rice-20% barley, and the last was the 80% rice-20% wheat group. 2. It was similar in the contents of plasma free basic amino acids of every diet group. The contents of Lys was highest and Arg, His were low in order. The mixed diet of 80% rice-20% barley group was higher than the rice only diet group in the contents of Lys and His. but rice only group was highest in Arg. The mixed of 80% rice-20% wheat diet group was lowest in the contents of Lys, His, Arg. Therefore feeding mixed diets of rice and cereals. the contents of Lys was highest, the second was Arg and the last was His in the plasma free basic amino acids level.