A field experiment was conducted at CCSHAU Rice Research Station, Kaul during kharif (rainy) seasons of 2006 and 2007 to evaluate the efficacy of new herbicide penoxsulam with different rates and time of application in transplanted rice. Weeds caused 30 to 32% loss in grain yield in weedy check as compared to weed free treatment. Higher doses of penoxsulam i. e. 0.0250 kg/ha (1-5 DAT) and 0.0225 kg/ha (8-12 DAT), while at par with each other and also with hand weeding twice (20 and 40 DAT), proved significantly better in controlling grassy, sedges and broadleaf weeds and provided significantly higher grain yield (similar to hand weeding and weed free treatments) and higher weed control efficiency than the standard herbicide butachlor at 1.5 kg/ha (1-3 DAT). The lower doses of penoxsulam i. e. 0.0225 kg/ha (1-5 DAT) and 0.0200 kg/ha (8-12 DAT) were, however, similar to butachlor. The study also revealed that comparatively lower doses of the herbicide could be used when it was applied at early post emergence (8-12 DAT).