To evaluate the efficacy of recently introduced herbicide trifloxysulfuron sodium in weed control in cotton fields, three experiments were carried out in 2003 in three cotton growing areas of Iran, including Varamin, Khorasan and Fars. In these experiments, the effects of trifloxysulfuron sodium at 7.5, 11.25 & 15 g ha-1, alone or tank mixed with cytogate at 2% (v/v), was compared with trifluralin at 0.96 & 1.2 kg ha-1, ethalfluralin at 0.99 & 1.16 kg ha-1 and diuron at 2.4 kg ha-1. Application time for trifluxysulfuron sodium was at 7-leaf stage of cotton, for diuron was pre-emergence and for trifluralin ethalfluralin was pre-planting soil incorporation. In all experiments, the effect of herbicides were compared with hand weeding (weed free) and weedy check. All herbicides, compared to weedy check, significantly reduced the number of plant and dry weight of Amaranthus retroflexus, A. blitoides, Chenopodium album, Portulaca oleracea, Acropliton repense, Alhagi camelorum, Eragrostis poaeoides, Echinocloa crus-galli, E. colonum, Sorghum halepense and Cyperus rotundus. Trifloxysulfuron at 11.25 or 15 g ha-1 was in most cases, more effective than its application at 7.5 g ha-1. In most cases, addition of cytogate enhanced the efficacy of trifloxysulfuron. Cotton injury was observed 1-2 weeks after application of trifluxysulfuron but did not adversely affect the crop productivity. All herbicides, compared to weedy check, increased the yields.