Abstarct: Nowadays, salt stress causes widespread damage to plants worldwide and it is one of the most important problems in agriculture. On the other hand, in recent years the role of symbiotic fungi as well as polyamines in increasing plant tolerance to saline conditions has been considered. Therefore, the present study was conducted to evaluate the effect of endophytic fungi symbiosis and spermidine foliar application on the growth of Stevia plant in response to salinity stress in two greenhouse and field experiments. In the greenhouse section, a factorial arrangement baxsed on completely randomized design (CRD) was carried out with three replications and three factors including salinity (0, 6 and 12 dS.m-1), fungal symbiosis [(non-inoculation, Piriformospora indica (Pi), Trichoderma virens (Trich), and co-inoculation of two fungi (Pi+Trich)] and spermidine foliar application (0, 0.75 and 1.5 mM). The field experiment was conducted as a split factorial arrangement baxsed on randomized complete block design (RCBD) with three replications. The levels of filed experiment factors were selected baxsed on the results obtained from the greenhouse section. Experimental factors included salinity (0, 6 and 12 dS.m-1) as a main plots and fungal symbiosis (non-inoculation and inoculation of P. indica + T. virens) and polyamine spermidine foliar application (0 and 0.75 mM) as a sub plots. Results of greenhouse and field study showed that inoculation with endophytic fungi and application of spermidine under salinity stress significantly improved stevia growth traits such as plant height, leaf area, fresh and dry weight of leaf, stem and shoot. Fungal symbiosis under salinity stress in greenhouse and field experiments showed a positive effect on most chlorophyll fluorescence parameters including Fm, Fv, Fv/Fm, Y(II), Y(NO) and NPQ. Fungal symbiosis treatment and spermidine application increased proline accumulation and relative water content (RWC) and reduced electrolyte leakage (EL). The results also showed a significant increase in antioxidant enzymes activity such as SOD, CAT, POD and APX and a decrease in the amount of H2O2 due to fungal symbiosis and spermidine spraying in both experiments, which reduced the adverse effects of salt stress on membrane lipids. Irrigation with saline water, especially 6 dS.m-1, increased the leaf stevioside and rebaudioside A concentration and also fungal symbiosis treatment and application of polyamine spermidine stimulated further accumulation of these compounds. Therefore, application of these fungi in combination with foliar application of polyamine spermidine can improve the growth, physiological and biochemical characteristics of stevia medicinal plant under salt stress conditions and increase the production of glycoside compounds by increasing plant tolerance.