A field experiment was conducted at Jimma University College of Agriculture and Veterinary Medicine research field from October 2011 to March 2012 under irrigation to assess the response of onion to farmyard manure and nitrogen fertilizer rates. The study consists of four levels of FYM (0, 15, 30 and 45 ton FYM ha-1) and four levels of nitrogen (0, 50, 100 and 150 kg N ha-1). The experiment was conducted in 4 × 4 factorial arrangements in a randomized complete block design with three replications. Data on growth, yield, and quality parameters were recorded and analyzed using SAS Computer Software version 9.2. Results revealed that interaction of FYM and N fertilizer significantly (P < 0.05) influenced Plant height, number of leaves, leaf lengh, maturity, average bulb weight, total yield, marketable yield, harvest index, bulb dry matter, TSS and split bulbs. However, leaf diameter, bulb length, bulb diameter and unmarketable yield were not affected by the combined application of FYM and N fertilizer. The findings highlighted that the performance of onion at Jimma area can be enhanced through application of FYM and N fertilizers.