The allelopathic potential ( E. colona (L.) Link. one of the most temportant weeds of rice, was evaluated by in vitro bioassay techniques. Rice variety ‘Kranti’ seeds were allowed to grow for 5-7 days in petri dishes with filter paper, soil or soil plus activated charcoal along with decomposing or decomposed leachates of the weed (obtained from 20, 30, and 40 or 60 days old plants). Observations of allelopathic effects on germination and root and shoot growth were recorded. The allelopathic effects of leachates increased with increasing concentrations (1, 2.5, 5, and 10% w/v). The decomposed leachates were found to be more toxic than the decomposing ones. Rice root growth was completely inhibited with 10% w/v leachates of 60 days old plant. The decomposing and decomposed leachates reduced rice shoot growth by 57% and 84% respectively. In soil medium the allelopathic effects were considerably reduced. Addition of activated charcoal to soil completely reduced the adverse effects on germination and seedling growth of rice.