In order to understand the effects of enhanced ultraviolet-B (UV-B) radiation on soybean yield components and seed growth characteristics, three determinate soybean cultivars, Hai339 (H339), Heinong35 (HN35) and Kennong18 (KN18) were grown for 2 years in a field experiment exposed to enhanced UV-B radiation. Enhanced UV-B radiation decreased plant height, dry weight of individual stem and yield per plant of three soybean cultivars on average by 15.5%, 16.9% and 43.7%, respectively. Pod number per plant was the most responsible component for yield change under UV-B radiation in the 2-year study. Seed number per pod was less affected by change in light treatment in our experiment, compared with the pod number per plant. UV-B radiation had no significant effect on effective filling period, however, seed size was negatively impacted by UV-B radiation and it decreased 12.3% for three soybean cultivars. Reduction of seed size was mainly due to the decrease of cotyledon cell number. Enhanced UV-B radiation had no significant effect on cotyledon cell volume, cell growth rate or cell weight. Our results suggested that the reduction of seed ABA concentration was directly responsible for lower cotyledon cell number under enhanced UV-B radiation.