The experiment was carried out at ‘C’ Block Farm of BCKV, Nadia,West Bengal, India for two consecutive years to study the efficacy of some herbicides on growth and yield of onion cv. Sukhsagar. Eight treatments were included. The experiment was laid out in RBD with 3 replications. The treatments were: T1- Oxyfluorfen 23.5% EC as preplanting and at 30 DAT, T2- Oxyfluorfen 23.5% EC as pre-planting + Quizalofop Ethyl 5% EC at 30 DAT, T3- Oxyfluorfen 23.5% EC + Quizalofop Ethyl 5% EC at planting and at 30 DAT, T4- Pendimethalin 30% EC as preplanting and at 30 DAT,T5- Pendimethalin 30% EC as pre-planting + Quizalofop Ethyl 5% EC at 30 DAT,T6- Pendimethalin 30% EC + Quizalofop Ethyl 5% EC at planting and at 30 DAT, T7- Oxyfluorfen 23.5% EC as preplanting + hand weeding at 30 DAT and T8- Weedy check. The results revealed that application of pendimethalin (T4) recorded maximum plant eight (59.42cm), leaf number (7.17), bulb weight (76.06g), marketable yield (22.95t ha-1) as compared to minimum values of 50.08, 5.33, 54.44g and 13.81 t ha-1 under weedy check plots. The total dry weight of weeds was lowest (10.94g m-2) under T7 treatment followed by T4 (16.66 g m-2) and T5 (19.51 g m-2). The same trend was also noticed in case of weed control efficiency i.e., maximum value (90.21%) in T7 followed by T4 (85.12%) and T5 (82.44%). The highest additional benefit (Rs. 45750.00 per ha) over control was recorded in T4 treatment. The pendimethalin may be recommended as most effective herbicide for onion cultivation under alluvial zone of West Bengal.