The allelopathic effect of saponins isolated from methanolic extract of Trigonella hamosa and Solanum lycopersicum (donor species) on germination and growth of Allium cepa (recipient species) was investigated in this study. Results revealed that saponins significantly inhibited seed germination and plumule growth rate of Allim cepa. Germination percentages of seeds treated with high concentration of S. lycopersicum and T. hamosa saponins (0.5 %) were 46 % and 40%, respectively, with a significant negative correlation (p< 0.05). Inhibition of growth rate was more noticed in case of seedlings treated with S. lycopersicum saponins than that treated with T. hamosa saponins. The relationship between the variation in saponins concentration and both germination and growth rate of A. cepa seedlings was significant (p< 0.05) as evaluated by ANOVA analysis.