Seed potassium contents in 6 wild rice, 53 japonica rice, 153 indica rice and 28 indica hybrid rice from 25 countries and areas were determined in flame photometry. The average seed potassium contents of the four kinds of rice were arranged in such order: indica hybrid combinations, japonica>indica>wild rice. The both extremes of the seed potassium contents in japonica, indica, wild rice and indica hybrid genotypes were 0. 4774 % and 0. 2175%,0.4495 % and 0.2165 % , 0. 2508 % and 0. 1381 %, and 0. 3763 % and 0. 3018 %, respectively. The genotypic differences were high significant. The frequency distribution of the seed K contents in the 234 cultivated genotypes resembled normal distribution.