A field experiment was conducted in Uttar Pradesh, India, in sandy loam soil during 1997-2000 to investigate the critical period of crop weed competition in sugarcane ratoon. The treatments were: weedy and weed free up to harvest; and weedy and weed free at 30, 60, 90 and 120 days after ratoon initiation (DAI). Weed free treatments at 30, 60 and 90 DAI resulted in reduction of weed dry matter at 60, 90 and 120 DAI. The highest amount of weed dry matter (19.1 g/m²) was at 30 and 60 DAI. Weed free up to 60 DAI onwards significantly increased ratoon yield compared to weedy up to harvest. Results indicated that the critical period of weed competition was between 27 and 50 DAI.