Allelopathic effects of aqueous and methanolic leaf extract of invasive tree para rubber is assayed in the laboratory condition on germination and seedling growth of four commonly cultivated leguminous crops of Tripura. Both the extracts were strongly hinder the seed germination and seedling growth of Cicerarietinum, Lens culinaris and Vignaradiata, applied in very lower concentration (0.62-2.5% aqueous and 0.1mg/ml – 0.5mg/ml methanol extract). With the increase of concentration, germination, radical and plumule growth of these three species were highly reduced and no germinations were recorded in the experimental sets treated with 5% aqueous solution. Our study reveals that one of the test crop V. mungo is resistant to that effect, in which IC50 values for germination was recorded very high (25.89%). Our investigation also showed that, aqueous extract has strong allelopathic potentiality than the methanolic extract. This allelopathic potentiality may be the one of the causes and consequences of rubber plantation that does not support the understory vegetation. The result of this investigation may be utilized in the field experiment and the selection of its coexisting species with rubber plantation for the production of herbage and fodder.