a b s t r a c tNine soybean cultivars widely cultivated in Northeast China were investigated in present study to assess their O 3 sensitivities on the basis of the response of photosynthesis and seed yield to ambient and future ozone (O 3 ) concentrations, and determine whether the effects of O 3 vary with the developmental stages (flowering and seed filling stages). Relative to charcoal-filtered air (CF), elevated O 3 concentration (E-O 3 , ambient air + 40 ppb) significantly reduced soybean yields by 40%, with a range of 32-46% among cultivars. E-O 3 also induced significant decreases in pigment contents, net photosynthetic rate and chlorophyll a fluorescence at both flowering and seed filling stages in most cultivars. Except net photosynthetic rate and stomatal conductance (g s ) at seed filling stage, all variables showed no significant interaction between O 3 and cultivar, suggesting that all tested cultivars had similar sensitivities to O 3 . The responses of seed N content to E-O 3 differed among cultivars. Ambient O 3 concentration (mean of daily concentration of 19 ppb) did not induce any change relative to CF. Significant positive relationship between endogenous g s in CF and yield loss among cultivars was found only at seed filling stage. Positive correlation between effects of E-O 3 on leaf N content and effects on light saturated photosynthetic rate (A sat ) indicated that g s and leaf N content at seed filling stage contributes to yield loss and decreased photosynthesis by E-O 3 , respectively. It can be inferred that E-O 3 had a larger negative effects on seed filling stage than flowering stage of soybean.