Allelopathic effect of basil (Tulsi) (Ocymum sanctum) on the germination of some weed species was evaluated. The germination of radish, redroot pigweed, hairy beggarticks and guineagrass was completely inhibited with addition of 7.5 g basil leaf powder to 100 g of sand as compared to plants grown in sand alone or in a mixture of sand and sphagnum. The germination of seeds was significantly inihibited in redroot pigweed (13%) and hairy beggarticks (12%) when grown in 10% (w/v) basil leaf extract as compared to distilled water. Significantly lower germination of 58, 47 and 45% with basil stem+root extract (at 2.5% w/v) was recorded, respectively, in radish, redroot pigweed and hairy beggarticks. The length of radicle+root in case of redroot pigweed and hairy beggarticks was significantly lower in basil stem+root extract (2.5% w/v) than in distilled water and was significantly reduced further when the extract concentration was increased to 5% (w/v).