The leaf photosynthetic rate of pot-cultivated rice plants was measured under the condition of artificial lighting and, at the same time, its relations to their some relevant characters were examined with five different varieties of rice plants, Musashikogane, Akenohoshi, Sweon 262, Nanking 11, and RP 9-3. In the case of low light intensity (10 klx), no striking difference in the photosynthetic rate among the varieties was found in the period from the maximum tiller number stage till the heading stage, whereas in the ripening stage the rate of all the varieties dropped remarkably. In the case of high light intensity (60 klx), the photosynthetic rate decreased as the growing stages proceeded.The japonica type varieties had a high photosynthetic rate at the maximum tiller number stage, while the indica-japonica hybrid variety had high rate in the booting stage. Nanking 11, an indica type variety, showed a photosynthetic rate similar to that of the japonica type varieties. Sweon 262, an indica-japonica hybrid variety, seems to have a high photosynthetic ability compared with the japonica type varieties. In the change of respiration rate according to the number of days after transplanting, it was observed that the respiration rate of the japonica type and the indica-japonica hybrid type varieties decreased more than that of the indica type varietics. The respiration rate of all the varieties tested decreased according to the number of days after transplanting. A close correlation was observed between chlorophyll contents and the photosynthetic rate at 60 klx.