<p>This work was designed to study the effects of exogenous calcium (Ca) and penconazole (PEN) on the tolerance of walnut plants to salt stress and the physiological mechanisms underlying salt tolerance. Walnut plants under salt stress were treated with 15 mg L⁻¹ of PEN and 15 mM of CaCl₂. Our results showed that Ca, PEN and the combined application of Ca and PEN influenced the adaptive mechanisms in leaf and roots of walnut plants under saline conditions. Treatments increased photosynthesis pigments as well as osmotically active substances such as proline and soluble sugars and the combined application of both Ca and PEN was more effective than their single treatments. Salt stress-induced oxidative stress was evaluated as hydrogen peroxide content and lipid peroxidation (MDA). Ca and PEN mitigated the oxidative stress in the leaf by increasing the components of the enzymatic and non-enzymatic antioxidant system, but in the root, Ca and PEN decreased the oxidative stress by inducing the components of the enzymatic antioxidant system. Therefore, application of Ca and PEN reversed the salt-induced changes by inducing osmoprotectants, increasing components of the non-enzymatic antioxidant system and activating antioxidant enzymes.</p>