In a high-temperature greenhouse environment, the characteristics of the high-temperature-ripening Oryza sativa variety Fusaotome were investigated. At the full heading stage, the roots of this variety were more elongated at a depth of <5 cm than those of the normal-temperature-ripening variety Akitakomachi. During the ripening period, the sap bleeding rate of Fusaotome under high-temperature conditions was significantly higher than that of Akitakomachi, and the rice root activity of Fusaotome was higher. At high temperature, the panicle temperature of Fusaotome was significantly lower than that of Akitakomachi, whereas the relative light intensity of Fusaotome was significantly higher than that of Akitakomachi at each height from 30–80 cm. Under normal-temperature conditions, there was no significant difference in the leaf area index (LAI) between the two varieties at each height. However, at high temperature, the LAI of Fusaotome was significantly lower than that of Akitakomachi at >70 cm (top layer), 60–70 cm, and 50–60 cm. With the high-temperature treatment, the occurrence of milky white and basal white rice was significantly lower in Fusaotome than that in Akitakomachi. In contrast, there was no difference in brown rice yield between the two varieties under normal- and high-temperature conditions. These results indicate that the high-temperature-ripening O. sativa variety Fusaotome has vigorous root elongation and activity, relative to that of the conventional variety Akitakomachi, under high-temperature conditions. Moreover, it is a favorable variety for ripening with a reduced increase in LAI in the upper layers of the vegetation community.