In our study, UV-B radiation had no significant effect on seed number per pod (Table 4). Herbert and Titch field (1982) reported that seed number per pod is a minor component determining the yield of soybean. However, the small tendency of decreased seed number per pod under UV-B radiation indicated that seed number per pod is strongly determined by the internal genetic mechanism,and is less influenced by environment condition. Seed size was negatively impacted by UV-B radiation in our experiment. UV-B radiation averagely decreased seed size of three soybean cultivars 12.3%. Chen et al. (2004) reported that seedweight of 20 soybean cultivars showed different sensitivity to UV-B radiation. The seed weight of the 15 soybean cultivars decreased quite significantly while the seed weight of five other soybean cultivars had no significant changes. Seed size was a function of the rate of seed growth and the duration of dry weight accumulation in the seed fraction and thereby the dry weight. Genetic differences inseed growth rate are controlled by the cotyledon cell number (Egliet al., 1981). In our study, UV-B radiation decreased seed growth rate of three soybean cultivars on average by 12.5%. Seed growthrate was shown to be a function of the cotyledon cell number and the supply of assimilates to the developing cotyledons