Germination tests and pot experiments were conducted to explore the allelopathic effect of aqueous extracts of S. nigrum on germination, growth and yield of Vicia faba (L.) and Phaseolus vulgaris (L.). Ten treatments including control were prepared by using extracts obtained from different parts of S. nigrum, including roots, leaves, and seeds at 3 concentrations (10, 40, and 60%) to conduct the germination test. The pot experiment was studied by incorporating powder of different plant parts into the soil at 3 concentrations (0.5, 1, and 1.5%). The results of the germination test revealed that the aqueous extracts of roots and leaves significantly reduced germination percentage, radicle, and plumule length of both beans. There was a direct negative relationship between germination test and the plant parts used, including their concentrations. However, seed extract showed a non-significant difference (p > 0.05). In the pot experiment, different powders of black nightshade incorporated into the soil decrease plant height, root length, fresh and dry weights. However, the number of leaves was not affected. Also, yield components were decreased with the highest concentrations used. The reduction of germination, growth, and yield of the broad and common beans increased with higher concentrations of root and leaf aqueous extracts, while that of seeds had limited effect. The strongest allelopathic effect of broad and common beans was caused by root extracts of the highest concentration.