Two field experiments were conducted during 2015/2016 and 2016/2017 seasons at Shandaweel Agriculture Research Station, Sohag Governorate, to study the effect of onion density and weed control treatments on vegetative growth, yield and quality of  onion. Split plot design with three replicates was used. Onion plant density (240 000, 300 000, and 400 000 plant/ fed.) occupied the main plots, whereas weed control treatments (hand hoeing (twice), Goal + Select (once), Goal + Select (twice), Ecopart + Select (once), Ecopart + Select (twice) and control) occupied the sub plots. Onion plants grown under the highest density (400 000 plants/fed.) attained the highest values of plant height and number of leaves/plant, while the lowest density (240 000 plants/fed.) attained the lowest values, in both seasons. Total yield/fed. for onion grown under high density were higher than those under other densities. Planting onion at low density recorded the highest values of single bulbs%, and double bulbs%, while planting at high density recorded the lowest values, in both seasons. The highest values of number of leaves/plant and bulb weight were obtained by application of Goal + Select (twice), in both seasons. Average bulb weight, marketable yield/fed., culls yield/fed. and total yield/fed. were significantly decreased under weed control treatment, in both seasons. From this investigation, it could be concluded that using of the highest plant density (400 000 plant/fed.) and application of Goal + Select (twice) could be recommended for the highest values of gross income, net benefit and the percentage of benefit/cost ratio.