Abiotic stresses including salinity are the major limiting factors of growth and crop production worldwide. Microbial endophytes as the most important soil microorganisms, by modifying plants at genetical, physiological and ecological levels increase their yield per area unit and provide the possibility of crop production in saline and arid soils or climates with biotic and abiotic stresses. The endophytic fungus, Piriformospora indica has a pronounced growth-promoting activity and also increases plant resistance to environmental stresses including salinity, drought and plant pathogens. We compared some growth parameters, physiological and biochemical responses such as total soluble proteins, Relative Water Content (RWC), lipid peroxidation, free proline content, and enzyme antioxidants (catalase, glutathione reductase, superoxide dismutase, ascorbate peroxidase) activity of p. indica–inoculated and non-p. indica-inoculated (controls) rice (Oryza sativa) under salt stress. The obtained results show that P. indica increase the biomass of aerial parts and root, total soluble proteins, Relative Water Content (RWC), free proline content and enzyme antioxidants activity of inoculated rice in compared to the controls. In contrast, Lipid peroxidation decreased in inoculated rice in compared to the controls. The obtained results of this research indicated that the effective role of this fungus to improve growth of rice under salt stress conditions.