The weed suppressive activity of crop residues has been attributed to the release of allelochemicals, and the allelopathic potential of mango leaves for weed management has been previously reported. Mango leaves were dried, powdered and extracted with a variety of solvents to produce 5 fractions. One fraction, exhibiting significant allelopathic activity was identified as mangiferin (1,3,6,7-tetra hydroxy 2-C-β-glucopyranosylxanthone). The allelopathic activity of mangiferin was studied by treating seeds of wheat, radish and okra with mangiferin and recording germination percentage and seedling growth after 7 days. Activity against wheat and radish could not be tested above 200 ppm mangiferin because of their sensitivity to Triton-X 100 used to solubilize mangiferin at higher concentrations. At 200 ppm, mangiferin had no effect on radish, but wheat germination was reduced to 60%, and root and shoot length were decreased, compared to the control. At 1000 ppm, mangiferin decreased okra germination to 90% and reduced root and shoot length. At 200 ppm, mangiferin reduced radish chlorophyll a content (by 41.66%) and chlorophyll b content (by 11.36%).