The whole-plant morphology, leaf ultrastructure, photosynthesis as well as enzyme activities of two tomato cultivars (Meifen-2 and Hongsheng) to differential light availabilities (450-500 μmol m-2 s-1, 75-100 μmol m-2 s-1) were examined in controlled environment. The results showed that the plant biomass and root/shoot ratio decreased and the specific leaf area increased significantly under the low light condition. There was a significant increase in malondialdehyde (MDA) concentration, superoxide dismutase (SOD) and peroxidase (POD) activities and decrease in soluble sugar and protein contents in LL-grown plants. For both cultivars, downregulation of photosynthesis and electron transport components were observed in LL-grown plants, the inhibition of the photosynthesis under the LL condition could be partially explained by the decrease of stomata density and by the changes of chloroplast.