It is expected by rice breeders and sake brewers to establish the simple means for evaluating the size of white-core in grains of rice for sake brewing. In this study, we measured the white-core of each grain in two cultivers, Ipponjime and Gohyakumangoku, by using the image analysis. The results showed that the relative size of white-core to the whole size of grain, i.e. white-core rate, varied widely from grain to grain (O - 100 % ) in the same cultiver. Although the average of white-core rate in lpponjime seemed to be larger than that in Gohyakumangoku, there was no significant difference between them. But the region where the white-core was expressed in grains was different between two cultivars. Then we divided a grain in four parts, i. e. the 1 st, 2 nd, 3 rd and 4 th quadrants, and examined relative size of white-core in each quadrant. The results showed that, in Gohyakumangoku, the white-core was expressed mostly in the 1 st and 2 nd quadrant, but in all quadrants in lpponjime