Salvia is one of the largest medicinal genera of lamiaceae family. Yield and quality of medicinal plants are affected by weed infestation. Herbicide application is necessary for commercial production of medicinal plants. Thus, the research includes two separated pot experiments based on completely randomized design with three replications was conducted to evaluate the response of Salvia aethiopis and S. nemorosa to some photosynthetic inhibitor herbicides.The first experiment contained five herbicides (bentazon, phenmedipham + desmedipham, metribuzin, oxyflurofen and oxadiargyl) in three rates (0.75X, 1X and 1.25X where X is equal to the recommended rate of herbicide) in order to select two herbicides with low and moderate effects.The second experiment consisted of two herbicides (bentazon and oxadiargyl) at five rates (0.5X, 0.75X, 1X, 1.25X and 1.5X) in order to evaluate the tolerance mechanism and determine the best herbicide rate in these species.The result from the first experiment showed that herbicide application led to increase in crop injury, minimum fluorescence (F 0 ) and malondialdehyde content (MDA) in spite of decrease in maximum fluorescence (F m ), maximum quantum efficiency of PS?? (F V /F m ), SPAD value, relative water content (RWC), plant height and shoot and root dry weight as compared to the control in both species. Finally, bentazon (minimal injury) and oxadiargyl (medium injury) were selected in bothe species. In the second experiment the herbicide application led to increase in crop injury, minimum fluorescence (F 0 ) and malondialdehyde content (MDA), antioxidant enzymes activity such as catalas (CAT), ascorbat peroxidase (APX) and guiacol peroxidase (GPX) and essential oil content in spite of decrease in maximum fluorescence (F m ), maximum quantum efficiency of PS?? (F V /F m ), membrane stability index (MSI), relative water content (RWC), chlorophyll and carotenoid contents, plant height, shoot and root dry weight and essential oil yield as compared to the control in both species. Finally, bentazon with minimal injury and the lowest rate of herbicide (0.5X) were recognized as the best type and the best rate of herbicide in both species respectively. According to the results of the two experiments, S. aethiopis is more tolerant to herbicide treatment as compared to S. nemorosa . Bentazon is Probably a suitable herbicide for selective weed control in both species. Key Words Medicinal plants, Salvia, Herbicide tolerance, Oxidative stress, Chlorophyll fluorescence
