Humic acid (HA) efficiently enhances the uptake of nutrients of plants, especially on saline soil. In this study, some nutrient contents of onion in response to salinity and HA application were investigated, and effects of HA application on salinity resistance was evaluated. Research plots were established as a randomized factorial design with four replications on a lysimeter and each replication included 10 plants. Plants in the lysimeters were irrigated with tap water (control, EC: 0.3 dS m(-1)) and four different doses of salinized water (EC: 2.0, 4.0, 6.0 and 8.0 dS m(-1)). The HA (0 and 1.0 g kg(-1)) was applied to the soil and mixed with the soil before planting. Increasing the levels of irrigation salinity decreased contents of K, Ca, N, P, Mg, Fe, Zn, Cu and B in onion bulbs; increased contents of Na, Cl and Mn. However, the highest content of K, Ca, and N in the bulbs were obtained by HA application under different salinity levels. Similarly, the soil application of HA positively was affected the P, Mg, Fe, Zn, B contents of the bulbs. While contents of Na, Mn, and Cu were not affected by soil application, Cl was decreased. The results showed that application of HA could partially reduce the harmful effects of salt, so HA can be used as an alternative method to improve product performance in saline conditions.