The current study is carried out to investigate the response of photosynthetic efficiency of soybean plant to drought stress extended for six days. Plants exposed to water deficit, growth inhibition and chlorophyll content losses increased. All drought treatments resulted in distinct physiological and biochemical effects on photosynthesis in a duration dependent manner. Relatively high inhibitory effect was observed throughout the experimental period, six days drought almost totally crushed the dynamics of chlorophyll accumulation in soybean leaves. A marked decrease in the ratio of chlorophyll a/b occurred in 6 days drought treated soybean leaves. Thus, a significant reduction in content of aminolaevulinic acid (ALA) was observed after 6 days drought treatment compared with relatively less decrease after 2 and 4 days drought treatments. The maximal photochemical efficiency of soybean leaves subjected to drought treatment, decreased sharply in Fv/Fm values to approximately half of the corresponding control at the end of drought duration. The photosynthetic strength of the plant indicated by Fv/F0 values showed that, soybean leaves exposed to drought were significantly decreased especially at the end of experimental period. Drought stressed soybean leaves showed a highly significant increase in H2O2 and MDA contents reached about 4.5 fold increase relative to control after 6 days drought treatment. This means that drought caused depression of photosynthetic efficiency of soybean leaves in a period-dependent manner.