The physiological characteristics of flag leaves of rice variety "Jiyou 1" at full heading time under saline alkali stress,such as net photosynthesis rate （Pn）,stomatal conductance （Gs）,transpiration rate （Tr）,intercellular CO₂ and concentration （Ci） were measured with LI-6400 Potable Photosynthesis System under simulated light intensities from 0 to 200 μmol photon m^-2s^-1.The results showed that in any case Pn,Gs and Tr increased sharply as the light intensity enhanced from 0 to 1 500 μmol photon m^-2s^-1,whereas Ci decreased significantly.Pn,Gs and Tr increased slowly and Ci reduced slowly as the light intensity enhanced from 200 to 800 μmol photon m^-2s^-1.As the light intensity exceeded 800 μmol photon m^-2s^-1,Pn,Gs and Tr reached maximum respectively and tended to dynamic balanced or decreased slightly,while Ci reduced to minimum and kept a balance.Compared with the control,Pn,Gs,Tr and Ci of saline alkali stressed rice entirely decreased.The light saturation point and light compensation point of photosynthesis were significantly lowered under saline alkali stress.