The Floristic composition of weeds in five different rice field around Vanur taluk of Villupuram district, Tamil Nadu, India was studied from November 2010 to April 2011. A total of 56 weed species belonging to 23 families was identified. Out of this 37 species in Kiliyanur, 38 species in Konthamur, 45 species in Thensiruvallur, 30 species in Thailapuram, and 32 species in Aadhanapattu were identified. An important value index for each weeds species was calculated to find dominance. Bergia capensis, Cynodon dactylon, Cyperus difformis, Eclipta alba, Echinochloa colona, Marsilea quadrifolia were dominant weeds species. Considering species diversity, Thensiruvallur village rice field was highly diverse of weed species compared to other fields. From the six month observations, it was found that weed growth occurs within forty one days after rice sowing. The perennial weeds created the most serious problem in rice fields.