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Effects of soil-moisture stress at different stages of soybean [Glycine max.(L.) Merr development on yield and yield components such as number of nodes per plant, number of pods per node, number of seeds per pod and seed weight were studied. This experiment was conducted in the experimental farm of college of Agriculture, Isfahan University of Technology, with 8 main irrigation treatments, 2 soybean cultivars of Clark and Williams, and 4 replications in 1985 and 1986.The results showed that moisture stress had significant effects on soybean yield and yield components. In all moisture—stress treatments, number of nodes per plant decreased. In maturity stage, moisture—stress decreased seed weight. In all treatments, yield of Clark cultivar was greater than Williams and this difference was due to the yield of secondary branches. Soil—moisture stress was also effective on branches and decreased pod number, weight of pods, number of seeds per pod and seed weight