Field trials were conducted between 2010/11 and 2011/12 at the Forestry Research Institute of o Nigeria (FRIN) of Federal College of Forestry Mechanization Afaka, Kaduna experimental site, 10 1o 1 03 N, 07 21 E and 644m above sea level in the Northern guinea savanna agro-ecological zone during 2011 to 2012 dry season. The objective was to evaluate the effect of different concentration and frequency of foliar application of Moringa extract on growth and yield of Onion (Allium cepa Lam). Fresh Moringa oleifera shoots were obtained from experimental site of the College when it was 35 days old, air dried for some days and crushed with water (10kg of dry material in water) in a household blender for 10 minute. The solution was filtered through a filter paper (Whattman No 42) and the liquid extracts obtained were diluted with water to produce the treatments. The treatments consisted of four concentration 2% (1 litre of extract/50 litre of water), 4% (1 litre of extract/25 litre of water), 3.2% (litre of extract/31 litre of water), 3.7% (1 litre of extract/27 litre of water) and a control (no extract) and two frequency of foliar application once (3weeks) and twice 3 and 6 weeks after transplanting. The trial was laid in a Randomized Complete Block Design(RCBD) and replicated three times. Data were collected on number of leaves/plant, plant height and crop vigour score at 5, 7 and 9 WAT. The data collected were subjected to analysis of variance. Result obtained showed a significant (P = 0.05) effect of the treatments on the characters measured with moringa extract concentration ratio of 1:2 (50%) and frequency periods of foliar application at 3, and 6 weeks after transplanting manifesting the highest effect. Based on the result, application of Moringa extract concentration ratio of 1:2(50%) and frequency period of foliar application at 3, and 6 weeks after transplanting of onion should be adopted for use in Northern guinea savannah ecological zone on the variety of onion tested, since it is easier to get Moringa all year round and in large quantities for large hectare of farm land.