High allelochemic contents exhibited in leaves of an upland weed, Eupatorium adenophorum Spreng. were extraced with methanol. Testing on seed germination inhibition with 19 species of crops and weeds, it showed that 9 species were strongly inhibited (90-100%) while the other 3 and 4 were moderately (50-89%) and slightly (10-49%) affected respectively. Purification of methanol extract was employed by solvent partition with petroleum ether and ethyl acetate respectively. Furthur purification by silica gel column chromatography was done by eluting with acetone at the concentration of 100, 50 and 0 percent, Every fraction obtained was parallel tested. The eluent of 100% acetone from both aqueous and ethyl acetate fraction showed inhibition on root and shoot growth of Nam Ru rice (ORYZA SATIVA Linn. cv. Nam Ru) and Dactyloctenium aegyptium which represented of monocot crop and grass while eluent of 50% acetone from aqueous fraction affected on root and shoot of Mimosa invisa Mart. Which represented dicot weed. However, it is obvious that the higher degree of inhibition is on the root growth rather than the shoot growth. Moreover, it was found that 9 tested crops and weeds were inhibited on growth when they were planted on soil mixed with 5-10% of dry E. adenophorum.