The experiment was conducted to evaluate the efficacy of post emergence applications of imazethapyr on weed control and soybean yield. The field was infested with grassy weeds (51.6%), broad leaf weeds (34.1%) and sedges (13.2%). Application of imazethapyr XL 10% SL at 150 g/ha as post emergence significantly reduced the density of all grassy, broad leaf weeds sedges and their dry weight, and provided maximum number of branches/plant, pods/plant, seeds/pod and seed yield as compared to weedy check and imazethapyr 10% at 50 g/ha. Infestation of weeds throughout the growth period caused 57.2% reduction in seed yield of soybean. Maximum seed yield (1075 kg/ha) and weed control efficiency of grasses (86.9%), broad leaf (88.4%) and sedges (73.0%) was obtained with 2 hand weeding at 20 and 40 days after sowing closely followed by imazethapyr XL 10% at 150 g/ha (957 kg/ha). Application of imazethapyr XL 10% SL at 100 g/ha recorded significantly higher net return (Rs 14,237/ha) and B : C ratio (1.68) followed by imazethapyr XL 10% at 150 g/ha over weedy check and imazethapyr XL 10% at 50 g/ha.