Abstract: The effects of light intensities,temperatures,pH and salinities on photosynthesis of Chlorella sp.XQ200419 and Chlorella marina NJ016 were studied by measuring net photosynthetic O2 evolution.For Chlorella sp.XQ200419,the suitable light intensities ranged from 100 to 1600 μmol•m-2•s-1,and the saturation light intensity is about 500 μmol•m-2•s-1.The suitable temperatures ranged from 25℃ to 42.5℃,with the optimal temperature of 37.5℃.The suitable pH values ranged from 6.5 to 9.0,and the optimum is pH 70.The net photosynthetic O2 evolution decreased a little while the salinity increased from 0 mol/L to 0.6 mol/L.For Chlorella marina NJ016,the suitable light intensities ranged from 400 to 1600 μmol•m-2•s-1,and the saturation light intensity is about 1400 μmol•m-2•s-1.The suitable temperatures ranged from 25℃ to 42.5℃,with the optimal temperature of 37.5℃.The suitable pH values ranged from 5.0 to 9.0,and the optimum is pH 8.0.The net photosynthetic O2 evolution increased obviously while the salinity increased from 0 mol/L to 0.6 mol/L.The results indicated the basic physiological and ecological characteristics of the two Chlorella species:adapting to relatively strong light intensity,higher temperature,neutral to alkalescent conditions and higher salinity.However,there are some differences between these two species in their response to the change of environmental conditions.Compared with Chlorella sp.XQ200419, Chlorella marina NJ016 has higher saturation light intensity,and is able to adapt to much broader pH values.Besides,its photosynthesis is promoted by appropriate increase of salinity.It reveals that Chlorella marina NJ016 might have more potential for fast growth in cultivation. The results are helpful for optimization of culture conditions for Chlorella,and also valuable for selection of Chlorella strains suitable for mass culture.