We studied the allelopathic effects of Flemingia semialata Roxb. leaf aqueous extracts in laboratory bioassays and in pot experiments on the growth of maize (Zea mays L.) and rice (Oryza sativa L.). The leaf aqueous extracts stimulated growth and yield of maize but was inhibitory to rice. The 100 % concentration of extract was most inhibitory to the growth and biomass of rice. On the contrary, the extracts stimulated the growth and biomass of maize at all test concentration. Gas chromatography-mass spectrometry (GC-MS) analysis of F. semialata leaf litter revealed the presence of alkaloids, phenols, terpenoids, unsaturated fatty acids and many others compounds. The compounds detected in methanol extracts were : 2-Isopropyl-5-methylcyclohexyl 3-(1-(4-chlorophenyl)-3-oxobutyl)-C (38.36, %), in petroleum ether extracts major compound was : 2R-acetoxymethyl-1,3,3-h imethyl-4T-(3-methyl-2-buten-1-yl)-1T-cyclohexanol (24.04 %) and in chloroform extract major compound was : Z-2-Octadecen-1-ol (36.74 %). Allelopathic effects of extracts from the leaf of F. semialata may be due to the presence of above compounds identified by GC-MS analysis.