Two experiments with factorial arrangements on the basis of randomized complete block design in three replications were conducted in 2007 and 2008, to evaluate chlorophyll content index (CCI), fluorescence of chlorophyll, proline content and grain yield of three soybean cultivars (Williams, Zan and L17) under a non-saline (control) and three saline (3, 6 and 9 ds/m NaCl) conditions in the greenhouse. Six seeds were sown in each pot filled with 900 g perlite, using 144 pots in each experiment. After emergence, seedlings were thinned and four plants were kept in each pot. Zan had the highest leaf proline content, but the lowest CCI, chlorophyll fluorescence and grain yield per plant. However, these traits were statistically similar with those of L17 and Williams. The chlorophyll content index and fluorescence of chlorophyll in soybean leaves decreased with increasing salinity. Reduction in chlorophyll fluorescence due to salinity stress was related to the damage of chlorophyll under saline conditions. In contrast, leaf proline content increased as salinity increased. Mean grain yield per plant under salinity stress was much less than that under non-saline conditions. These reductions were closely related with low CCI and PS II activity (fv/fm) and high leaf proline content in soybean cultivars. It was concluded that soybean is a sensitive plant to salinity stress, but the extent of this sensitivity varies among cultivars.