This study was conducted during the seasons of 2011/2012 and 2012/2013 at the Experimental Farm of Shandweel station to investigate the effect of plant density (100, 80, 60 and 40 plants/m²) and set-size (10-15, 15-20 and 20-25 mm) on onion (Allium cepa L.) yield and some bulb characteristics of onion produced from sets under Sohag Governorate conditions. Results revealed that, total single bulbs and marketable yield were significantly increased at the density of 100 plants/m², while culls yield, doubling and average bulb weight decreased, also bolters reduced with plant density of 40 plants/m². Total marketable yields, average bulb weight and emergence were significantly increased by using large sets (20-25 mm). In the meantime, single bulbs were increased, while culls yield, doubling and bolters reduced by small sets (10-15 mm). Culls yield, bolters and bulb weight were significantly decreased by the interaction (100 plants/m² x small sets 10-15 mm).