The inhibitory effects of aqueous methanol extract of Cymbopogon nardus (L.) Rendle were determined on seedling growth of eight test plant species: alfalfa ( Medicago sativa L.), cress ( Lepidum sativum L.), lettuce ( Lactuca sativa L.), rapeseed ( Brassica napus L.), barnyard grass ( Echinochloa crus-galli L.), Italian ryegrass ( Lolium moltiflorum Lam.), jungle rice ( Echinochloa colonum (L.) P. Beauv.) and timothy ( Phleum pratense L.). The bioassay was conducted with four extract concentrations (0.01, 0.03, 0.1 and 0.3 g dry weight equivalent extract/mL). The extracts inhibited significantly shoot and root growth of four test plants such as cress, lettuce, rapeseed and Italian ryegrass at the concentration ? 0.03 g dry weight equivalent extract/mL. The inhibitions of shoots and roots increased with increasing extract concentrations. The concentrations required for 50% growth inhibition of all test plants ranged 0.007-0.090 g dry weight equivalent extract/mL. Roots of all test plants were more sensitive to the extract than their shoots. Lettuce was most sensitive, follows by cress and timothy. The results suggest that C. nardus may have allelopathic compounds and may be a candidate for isolation and identification of allelopathic compounds to develop an alternative weed management option.