A field trial was conducted at Holetta research center and farmers' fields during 2016/17 and 2017/18 to determine the effectiveness of S-metolachlor herbicide application on annual grasses and broad leaved weeds in faba bean. The experiment consisted of six treatments; S-metolachlor (1.0, 1.5 Lha^-1 alone and S-metolachlor 1.0, 1.5 Lha^-1 supplemented one hand weeding (25-30 days after crop emergence), farmers' practice twice hand weeding (25-30 and 55-60 days after crop emergence) and weedy checks arranged in randomized complete block design. The faba bean variety used was Dosha and the recommended fertilizer rate was applied. The herbicide was applied single pre emergence (1-3) days after planting using manual knapsack sprayer with a water volume of 200 Lha^-1 rates for each plot. The result exhibited that pre emergence application of S-metolachlor @1.0 and 1.5 Lha ^-1 had a significant (P< 0.05) effect on broad leaved and grass weeds; Polygonum nepalensis, Corrigiola capensis, Plantago lanceolata, Caylusea abyssinica, Spergula arvensis, Raphanus raphanistrum, Bidens pilosa, Galinsoga parviflora, Oxalis latifolia, and Guizotia scabra, Snowdenia polystachya, Setaria pumlia, Phalaris paradoxa and Avena fatua for a prolonged time after application and their density was significantly reduced. Between treatments significant differences of yield, plant height and seeds per plant was attained. The highest grain yield (2770 kg ha^-1) was achieved from twice hand weeding followed by S-metolachlor 1.0 and 1.5 Lha^-1 supplemented one hand weeding (2540, 2502 kg ha^-1). The yield advantages were 64.8, 61.6 and 61.0% over the unweeded check.