Abstract:The optimal temperatures for net photosynthesis and the quantum yield for CO2 uptake in rice seedlings are different. Both net photosynthesis and quantullm yield were declined along the similar trend, when the leaf temperature was below 20℃. Chilling treatment (6–12 ℃) at high light (1200 μmol•m-2•s-1) for 2 hours markedly inhibted quantum yield for 34%–74%, and 46%–89% of net photosynthesis. No any inhibition of quantum yield was observed under low light. (120μmol•m-2•s-1) during the chilling treatment, but 33% of inhibition occured as rewarming the leaves for 2 hours at 30℃ and low light. The short term treatment (2 hours) of leaves at the 8 ℃ and light intensity of 1000 μmol•m-2•s-1, then followed the increase in temperature (30 ℃) and decrease in light (12 μmol•m-2•s-1) resulted in a reversible change of quantum yield from 0.018 to 0.034 (after rewarming of 1 hour) and 0.039 (2 hours). Low oxygen (2%) reduced the inhibition of quantum yield during exposure of rice leaves to chilling temperature and high light. It is indicated that high light and oxygen are important factors to interact with chilling temperature, and the process of photoinhibition with photo-oxidative injury occurred at chilling and light stress in rice seedling.