Heat stress greatly effect on rice quality and yield. Therefore the breeding of heat tolerance rice is important against to global warming. To breed heat tolerance rice, we have to wait until rice harvesting time to check rice yield and quality. In order to select rice with high temperature adaptability more effectively, it is necessary to develop a method of early and easy selection without waiting for harvest time. When plant meets environmental stress, reactive oxygen species is generated then badly effect on plant metabolism. Chlorophyll content and chlorophyll a and b ratio also changed according to reactive oxygen species content. We analyzed the changes in yield and quality at high temperature, means temperature was 280C and daily difference of temperature was 100, using rice cultivars cultivated in Korea. Based on these results, we chose varieties which showing high or low quality and yield difference between normal and high temperature conditions. We sowed selected rice seeds and cultivated to make young rice plant. Then we analyzed the change of chlorophyll content in leaves according to temperature conditions in selected rice cultivars. Analyzing the results, rice cultivars with little change in yield and quality at high temperatures were found to have less chlorophyll changes in the leaves. And rice cultivars with more change in yield and quality at high temperatures were found to have more chlorophyll changes in the leaves. Analyzing the content of reactive oxygen species in rice cultivars, we found that the rice cultivars with showing less change of chlorophyll content also showed less reactive oxygen species content with high activity of antioxidant enzyme. Based on the above results, it was confirmed that it can be efficient to select the heat tolerance rice during ripening stage by analyzing the leaf chlorophyll content after high temperature using rice young plant.