Salt stress inhibits plant growth, its yield and quality. This study was carried out to study the effect of humic acid (HA) as a plant growth stimulant in alleviating salt stress in onion bulbs. The onion plants were grown to maturity in metallic containers filled with soil in greenhouse conditions, then subjected to five salinity levels [0.3 (control), 2.0, 4.0, 6.0 and 8 dS/m] using NaCl combined with or without the soil application of 1.0 g/kg HA. Increasing salt concentration reduced the yield and quality of the onion bulbs. HA application resulted in higher yield than non-HA for all salt levels tested. It also resulted in higher dry matter yield of the onion bulbs, as well as total sugar, vitamin C and protein contents under different salinity levels as compared to the control but the soluble solids content remained unchanged in response to the HA application. These results suggest that soil application of HA has potential in improving onion yield and quality under salt stress.