An experiment was conducted to study the production potential of rice under varying population densities of barnyard grass (Echinochloa crusgalli). There was a significant reduction in plant height, dry matter production as well as in yield by rice plant with increasing population density of barnyard grass from 25 plants/m² to 250 plants/m² because weed plants compete for growth factors like light, nutrients and space, etc. The reduction in dry matter was to the tune of 35.76, 32.26 and 35.80% in 250 plants of barnyard grass as compared to pure rice crop in 2005 and 52.11, 45.56 and 44.41% in 2006, respectively. A decreasing trend in panicle length, number of grains per ear, 1000 grain weight, grain and straw yield were observed as plant density of barnyard grass increased from 25 plants/m² to 250 plants/m² during both the years of investigations. At higher densities of barnyard grass, there was a gradual increase in dry matter production. Hence there was more suppression of rice crop at higher weed densities which resulted in significant reduction in grain yield of rice crop.