A field experiment was conducted to evaluate the efficacy of penoxsulam 0.97%w/w (1.0%w/v) + butachlor 38.8% w/w (40% w/v) 41% SE applied as pre-emergence( 0-7DAT) spray in standing water against complex weed flora in transplanted rice at CCS HAU Regional Research Station, Karnal during rainy (Kharif) seasons of 2015 and 2016. The crop was infested mainly with Echinochloa crus-galli (~15%), Ammannia baccifera (~70%), and Cyperus difformis, Cyperus rotundus and other sedges (~15 %). Penoxsulam + butachlor 41% SE at 820 g/ha being as good as weed free check provided almost complete control (98.1-98.5% WCE) of complex weed flora during both the years, and it was better than penoxsulam 22.5 g/ha (87-88%), butachlor 1500 g/ha (90%) and pretilachlor 1000 g/ha (91%). Penoxsulam + butachlor 820 g/ha resulted into the highest number of effective tillers and grain yield (5.43 t/ha in 2015 and 6.06 t/ha in 2016). It was superior to its lower doses (615 and 718 g/ha) and penoxsulam 22.5 g/ha during both the years, and butachlor 1500 g/ha during 2016. There was no crop phyto-toxicity of penoxsulam + butachlor 41% SE at 820 g/ha (X) and 1640 g/ha (2X). Weeds allowed to grow throughout the crop season reduced the grain yield to the extent of 27.3 and 32.9% during 2015 and 2016, respectively.