This study was conducted to investigate variations in nutritive value of protein by sequentially changing the protein ratio in several combinations of foods and to obtain a desirable mix ratio for enhancing the nutritive value of protein. “Protein score” (FAO, 1957) and “Amino acid score” (FAO/WHO, 1973) were used to evaluate the protein value. Combinations of foods were selected from daily diets of the Japanese; polished rice or bread with one or two other items such as egg, milk, cheese, sardine, flounder, beef, pork and soybean. The results obtained were; 1) Changes in protein and essential amino acid contents were obtained by calculating the content ratio of each of eight essential amino acids as against basic amino acids by sequentially changing the mix ratio of protein in foods. 2) Increase in protein in items such as egg, milk, etc. as against protein in rice or bread caused a rapid initial increase in the protein score and amino acid score. Subseqent changes in the two chemical scores of these mixed foods varied depending on combinations and chemical scores of the ingredients. 3) Lysine or sulfur-containing amino acid is not a first limiting factor for those having the higher chemical scores in combinations of two items of foods. Such combinations were usually those where proteins in other food items were 30-40% of that in polished rice, and 40-50% of that in bread. These figures suggest the appropriate proportion of animal proteins to total dietary protein of two items of foods. 4) Variations in chemical score of protein in the combinations of polished rice or bread with two kinds of other foods were easily surmisable from those in the combinations.