The purpose of the present investigation was to make clear inheritance of high protein property and to obtain the informations on breeding of high protein rice variety. Parents used were a high protein variety "Brimful" (scented rice from Nepal) and a Japanese ordinary rice variety "Koshihikari". A cross was carried out in 1977 and progenies of F2, F3, F4 and F5 were grown from 1978 to 1981. The results obtained are summarized as follows : 1. The distribution in F2 and F3 populations of protein content was monomodal and symmetric. Mean of F2 population was located between a low protein parent and mid parent values (Fig. 1). It was suggested that high protein property was controlled by a number of multiple genes or polygenes. 2. The narrow sense heritability of protein content was estimated based on the variance and co-variance of F2 and F3 populations and the value was 0.589. 3. Regarding to the relation between protein content and agronomic characters, the results from F3 and F5 populations showed that the high protein property was not linked with agronomic characters and flavor in grains (Tables 2, 4 and 9). 4. As compared with F3 and F4 populations, F5 was high in mean value of protein content and also decreased in the genetic variance of protein (Tables 1, 3 and 8). The facts may be suggested that high protein property showed the tendency of genetic fixation in F5 generation. 5. In each of the F4 and F5 generations, significant difference was observed among the lines in lysine and threonine contents per dry weight, and the lines were far better than Koshihikari (Tables 5 and 10). But, there were not in the contents per protein. 6. Significant correlation was observed between protein content and lysine, threonine and methionine contents per dry weight in F4 and F5 populations (Tables 6 and 11). But, no correlation was observed per protein. 7. The promising lines which have high protein and also relatively good agronomic characters were selected based on the measured results in F5 population (Table 12).