This experiment was conducted to examine the influence of four plant growth regulators on growth, photosynthesis parameters and yield of soybean. To increase dry matter accumulation of seeds, some growth regulators were applied to field grown soybean cv. Sinpaldalkong #2 as determinate type and Muhankong as indeterminate type at dense planting condition. Choline caused significant reduction of stem length, but did not increase seed yield. The number of leaf and total leaf area were showed significant increase in all the treatments, but those increased tremendously in Muhankong treated with ethrel. CO2 assimilation and water use efficiency of a single leaf were showed the highest as 17.2 molm-2s-1 and 9.3 μ mmol mol-1 treated with mepiquat in Sinpaldalkong, respectively. The Photosynthetic rate was closely related to stomatal conductance, transpiration and water use efficiency. Mepiquat treatment mainly produced positive effects on the number of pods, percent of pod setting, number of seeds per pod in two cultivars and also increased their seed yield as compared with control.