Two field experiments were conducted at the Experimental Farm of the Faculty of Agriculture, Tanta during the winter seasons of 1995/96 and 1996/97, to study the effect of some nitrogen and sulphur sources on plant growth, yield and quality of onion. Nitrogen was supplied at level of 100 kg/fed. from four sources, i.e., urea, ammonium, sulphate, ammonium nitrate and calcium nitrate, while sulphur was supplied as a sulphur powder 50 and 100 kg/fed. or ammonium thiosulphate (ATS) 2 and 4 kg/fed.                 Results revealed that, ammonium nitrate increased average bulb weight while calcium nitrate increased the percentage of bolting plants. Addition of sulphur at 50 or 100 kg increased the yield of onion. Results showed also that NO₃-N was more accumulated in green leaves of onion than in its bulbs. The NO₃-N content in both bulbs and leaves was affected significantly by the nitrogen and sulphur sources. Ammonium sulphate as nitrogen source lead to less nitrate accumulation in onion plants followed by ammonium nitrate and urea, while calcium nitrate caused increasing accumulation of NO₃-N in plants. Sulphur treatment decreased the NO₃-N content of onion plants. Values of the interaction showed that ammonium sulphate was more effective on decreasing nitrate accumulation in the presence of sulphur treatments.