Mimosa pigra has been reported as an anvasive plant containing mimosine which has phytotoxic activity on weeds. In this study, the inhibitory effects of aqueous extracts from various plant parts of M. pigra were evaluated. The mimosine content was spectrophotometrically measured.  The phytotoxicity of the aquaous extracts was tested on radish, lettuce, and barnyardgrass. The results showed that mimosine presented in this plant varied from 24 to 53 mg/g DW, and the highest mimosine content was found in leaves (p0.05). These extracts at 10% concentration also caused a significant reduction in shoot length and fresh weight of radish. At the concentration of 10%, leaf, flower, and seed extract significantly inhibited all growth parameters including root length, shoot length, fresh weight and dry weight of lettuce while stem and fruit caused a dramatic decrease in root length, shoot length and fresh weight. The seed extract inhibited 100% of lettuce growth at 10% concentration. The extracts of M. pigra strongly suppressed the shoot elongation and biomass of barnyardgrass. The study confirmed the allelopathic activity of M. pigra, and it could be tested in the rice field for applying in green agriculture.