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Identifying the most suitable Brant's oak (Quercus brantii Lindl.) seed origins (provenances) due to the increase in the intensity of summer drought in the Zagros forests is very important for the reforestation issue. In this research, the physiological and biochemical responses of Brant's oak seedlings from eight provenances located in different altitudes and latitudes of Southern Zagros were investigated under drought stress (with the stopping of irrigation for one month). The data were analyzed in the factorial (2 levels of drought stress treatment and 8 levels of provenance), randomized complete design experiment by examining the simple and interaction effects of them. Also, drought resistance indexes of provenances were calculated and compared with each other by applying the photosystem II value before and after the stress. Results showed that severe drought stress significantly increased electrolyte leakage, osmolyte, Na, and proline contents in seedling leaves for all provenances. Although, the response of different provenances in terms of photosystem II was not similar. The provenances were located in lower altitudes (Basht site in Kohgiluyeh and Boyer-Ahmad province and Ghaemiyeh site in Fars province) and had higher resistance and resilience values due to adaptation to high temperature and or low precipitation. Also, Chitab provenance (a cold site with less dryness in Kohgiluyeh and Boyer- Ahmad province) became drought tolerant by closing its stomata during the day and thus reducing the photosystem II and improving it in the dark. Consequently, the drought resistance of Brant's oak seedlings is partly influenced by the seed provenances and climatic conditions. The use of these results can be recommended to managers in the reforestation of the Zagros forests. [ABSTRACT FROM AUTHOR]