Salinity stress is an increasing environmental problem for crop production worldwide. Already up to 20% of irrigated land is adversely affected by salinity, and the continuous accumulation of salt in cultivated soils as a result of irrigation and climate warming increases the signi?cance of this stressful factor. Pretreatment in plants is recognized as a valuable strategy to stimulate plant defenses, leading to better plant development under stress conditions. This study evaluated the effects of hydrogen peroxide (H 2 O 2 ) leaf spraying pretreatment on plant growth and investigated the antioxidative mechanisms involved in the response of pistachio plants to salt stress. Pistachio seeds were surface-sterilized and sown in sand moistened with distilled water and irrigated daily.Forty days after sowing, the seedlings were sprayed with distilled water (control) or 1, 5 and10 mM H 2 O 2 solution. At 24 h after the spray, the seedlings were treated with 0, 120 or 240 mMNaCl. Four harvests were performed to measure plant growth and some physiological and biochemical parameters. The ?rst harvest was forty days after sowing and before the spray; the second harvest was at 24 h after spraying onset and before salt addition; the third harvest was at 48 h after the spraying began, when the plants were subjected to saline conditions); and the fourth harvest was at 168 h after the start of spraying (6 days 240 Mm NaCl). Salt stress alone increased the levels of ionic leakage, proline, reduced sugar, reduced glutathione (GSH), H 2 O 2 , malondialdehyde (MDA) contents in leaves and sodium and chlorine concentrations in roots and shoots accompanying with increases in activities of some antioxidants such as ascorbate peroxidase (APX) and catalase (CAT). When H 2 O 2 -pretreated seedlings were exposed to salt stress, we obtained the higher activities of APX and CAT and as well got the enhanced levels of proline, reduced sugar, carotenoid, AsA and GSH in comparison to salt treatment alone. At the same time, pre-treatment with H 2 O 2 induced an additional increase of the potassium, while an additional decline was also observed in the sodium, chlorine, ionic leakage and MDA contents of pistachio seedling under salt stress. It was, therefore, concluded that H 2 O 2 ameliorated the stress generated by NaCl through the enhancing compatible solutes and antioxidants. Therefore, H 2 O 2 may participate in antioxidant enzymes and antioxidant compounds induced tolerance of pistachio seedlings to salt stress. Overall, the adverse effects of salt stress could be alleviated by exogenous application of H 2 O 2 . Keywords : Antioxidants, Oxidative stress, Salinity, Signal molecules.