Selenium (Se) at high concentrations can cause toxic effects in plants, whereas at low concentrations it enhances resistance to certain abiotic stresses. The possible mechanisms of the Se-enhanced tolerance of plants to salinity stress remain elusive. In this work, effect of Se supplementation at 0, 0.1, 1 and 10 mg l^-1 sodium selenate was studied in Lallemantia iberica plants subjected to salt stress. In pre-experiment design, The toxicity threshold for selenate was determined at the concentration of 10 mg l^-1, as the biomass of L. iberica plants decreased if selenate concentrations in the growth medium reached 10 mg l^-1. Thereafter, we used 0.1 mg l-1 Se to mitigate salt stress in L. iberica plants. Se at low concentration (0.1 mg l^-1) mitigated salt-induced oxidative stress because of the NaCl-induced lipid peroxidation was smallest in the plants treated with Se, and was highest in the plants grown without Se addition. This occurred as a result of glutathione (GSH) accumulation in Se-supplied plants. Additionally, Se-supplied plants exhibited higher glutathione peroxidase (GSH-Px) activity than –Se ones after 2 days salt stress. These data provided the first evidence that the low-level Se pretreatment alleviated salt stress in L. iberica by increasing GSH levels and by decreasing ROS production; and therefore less reduction of biomass production during salt stress.