Germination ability of rice seeds at a low temperature varies with the cultivars. However, the biochemical mechanism of this difference has not been clarified. To analyze the role of active oxygen-scavegning enzymes in germination at a low temperature, calatase activity in rice seed embryo was determined. The specific activity of catalase increased during germination and the rate of increase was high in cultivars with a high germination ability at a low temperature. Catalase activity was detected even in the embryo of dry seeds (before imbibition). This initial level of catalase also varied with the cultivars and there was a positive correlation between initial level of catalase activity and germination rate at a low temperature. Such a relation was not observed between the superoxide dismutase activity of dry seed embryo and germination rate at a low temperature. It was also found that cultivars with a high initial level of catalase activity in the embryo could germinate even in a 3 % hydrogen peroxide solution. These charac-teristics reflect one of the genetic traits of rice.