Abstract: We determined the chlorophyll content, activity of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD), as well as the gene expression of SOD, CAT and POD in rice flag leaves during the flowering stage under high temperature stress. We used real-time RT-PCR to disclose the mechanism of the physiological responses and adaptation of ‘Ⅱ YOU 838’ to heat stress. Upon heat treatment, the decline in chlorophyll content and the Chl a/Chl b ratio in ‘Ⅱ YOU 838’ was to a lesser degree than that of ‘Gang YOU 725’, and the activity of SOD and POD increased by a higher degree and the activity of CAT declined by a lower degree during the flowering stage. The expressions of the three antioxidative enzyme genes in ‘Ⅱ YOU 838’ were significantly higher than those in ‘Gang YOU 725’. These results implied that ‘Ⅱ YOU 838’ may have higher tolerance to heat stress by maintaining higher photosynthetic metabolism and improving protective antioxidant activity and expression.