Plant spacing determines to a greater extent crop performance in terms of growth and yield. The production of crop with organic fertilizer also plays a vital role in organic agriculture. Field studies were conducted to evaluate the effects of spacing and poultry manure on the growth, yield and quality of onion. Three spacing regimes were carried out consisting of 15 cm × 15 cm, 20 cm × 20 cm and 25 cm × 25 cm and four levels of poultry manure at 0, 5, 10 and 15 t /ha. The effects of spacing and poultry manure were evaluated for two years based on plant growth, yield, nutrient concentration, uptake and proximate composition of onion plant. Leaf thickness, bulb and shoot fresh weights were significantly increased by the wider spacing of 20 cm × 20 cm and 25 cm × 25 cm, compared with the narrower spacing of 15 cm × 15 cm in both seasons. However, the highest total dry yield (1.82 and 1.58) t/ha, shoot yield (2.31 and 1.32) t/ha and total fresh yield (13.69 and 12.55) t/ha were obtained with the spacing of 20 cm × 20 cm in both years. Similarly, application of poultry manure increased leaf thickness, bulb and shoot fresh weights and yields compared with the control. Generally, using 10 t/ha poultry manure has a superior effect on proximate composition and most of growth parameters and yield components achieved the highest nutrient concentrations and uptake on most of the macro and micronutrients in leaves and bulbs as compared with the control in both years.