Water deficit is the prime limiting factor in soybean production in semi-arid regions. Therefore, increasing soybean seed yield requires the selection of resistant and adapted cultivars to dry or water deficit conditions of Iran. In order to evaluate the effect of irrigation regimes on seed yield and yield components of three soybean cultivars an experiment was conducted in Lorestan University of Technology Research farm during the growing season of 2010-2011. The experiment was arranged as split-plot in the form of completed block design. Irrigation regimes were the main plots and the subplots were three soybean cultivars (M7,M9 and TMS). Then, irrigation treatments were conducted as follow; CI: applied 100% of water requirements during the whole season and RDI80, RDI70 and RDI50 applied 80%, 70% and 50% of water requirements, respectively. Based on the findings of this study, deficit irrigation had significant effect on the number of nodes, plant height, number of pods per plant, 100 seeds weight, grain yield and biological yield. Severe stress conditions had maximum effect on reduction in nodes number (10.54), plant height (44.24 cm), number of pods per plant (24.5), grain yield (1259.9 kg.ha^-1), biological yield (3013.2 kg.ha^-1) and 100 seeds weight (11.77 g). M9 cultivar had the most yield, biological yield, number of pods per plant, number of nodes, 100 seeds weight and water productivity in the water stress condition and non-water stress condition among the studies cultivars.