Onions bulbs are predominantly grown in the Northern parts of Nigeria. However efforts made at encouraging its growth in the South necessitates the identification of appropriate agro techniques. Plant population density is one of the most important factors influencing the size and yields of onion. Field trials were conducted during the rainy seasons of 2007 and 2008 at the National Horticultural Research Institute(NIHORT), Ibadan, forest agro-ecological zone of South Western Nigeria. The trial was a 2 x 3 factorial arranged in randomized complete block design with three replications. The first factor consist of two varieties (Red Creole and Violet de galmi), the second factor consists of three plant densities (26.6, 40 and 80 plants/m2). The results showed that irrespective of the population density, Red Creole and Violet de galmi did not differ significantly in plant height, Number of leaves and Neck thickness for both years (2007 and 2008). The highest yield for both years were recorded with Violet de galmi. However, they differ significantly in bulb weight and the yield. Irrespective of the Variety significant differences occurred in the Number of leaves , Neck thickness, Bulb weight and Yield. Interaction between Variety and Population Density was not significant for plant height but significant in the number of leaves, neck thickness, bulb weight and yield. Violet de galmi was identified as a better variety of onion for south western Nigeria. This can be grown at plant population of 80 plants/m2.