Onion is one of the most important vegetable crops produced in Ethiopia as well as in the Amhara Region by both small-holder farmers and commercial growers for both local and export markets. However, the productivity of onion is low due to inappropriate cultural practices including imbalanced nutrient supply in the soil. Therefore, a field experiment was conducted in Aradum Kebele of Raya Kobo District during the 2017/18 irrigation season to investigate the response of onion to different rates of farmyard manure and NPS: fertilizers. The treatments consisted of four levels of farmyard manure (0, 5, 10, and 15 t ha-1) and four levels of NPS (0, 100, 200 and 300 kg ha-1). The experiment was conducted in a 4× 4 factorial arrangement in a randomized complete block design with three replications. Data were collected on growth and yield parameters. The results of the present study showed that most growth parameters including plant height, diameter, and length of leaves, day to maturity, diameter, length and weight of bulbs, marketable, unmarketable and total bulb yields of onion were increased with increasing rates of NPS and FYM fertilizers. Plants without fertilizer recorded the minimum plant height and matured earlier. On the other hand combined application of 15 t ha-1 farmyard manure and 200 kg ha-1 NPS recorded the highest marketable bulb yield (29.60 t ha-1) followed by the combination of 15 t ha-1 FYM and 100 kg ha-1 NPS. The combined application of 15 t ha-1 farmyard manure and 100 kg ha-1 NPS recorded the highest net benefit with acceptable marginal rate of return value (1229.8% ) which can be recommended for economical production of onion in Raya Kobo District and areas with similar agro-ecologies. Keywords: Organic and inorganic fertilizer, plant height, marketable bulb yield.