In order to assess the impact of varying densities of jungle rice (Echinochloa colona) on rice, a field experiment was conducted at Directorate of Weed Science Research, Jabalpur farm in Kharif  2005 and 2006. With increasing population density of E. colona from 50 to 400 plants/m2, there was a significant reduction in LAI, biomass production as well as grain yield of rice due to competition from weed plants for growth factors like light, nutrients and space etc. The reduction in dry matter was to the tune of 32% with a E. colona density of 400 plants/m2 as compared to pure rice crop. Though the chlorophyll content of rice decreased with increasing density of E. colona but it maintained a higher chlorophyll content than E. colona. The increasing densities of E. colona significantly decreased various yield attributes of rice with the effect being more drastic on effective tillers/m2. The reduction in grain yield varied from 48 to 86% as the density of E. colona increased from 50 to 400 plants/m2.