Background: Nanosilver particles are among the potentially candidates for modulating the redox status and changing the growth, performance and quality of plants because of their physicochemical characteristics.

Objective: This study was carried out to elucidate the potential effects of nanosilver particles application on variations of photosynthetic pigments (chlorophyll and carotenoids) and essential oil content and composition of Pelargonium graveolens.

Methods: Four nanosilver particles (5 - 20 nm) concentration (0, 20, 40, and 80 mg.L^-1) were used as foliar application. The essential oils were isolated from aerial flowering parts of the plants by hydro-distillation method and then subjected to GC and GC-MS apparatus to determine the oil constituents.

Results: Chlorophyll and carotenoids content increased in leaves of nanosilver treated plants in compare with the control. Nanosilver application at 40 mg.L^-1 was the most effective treatments in pigments and essential oil content. Also, results showed that 26 components were identified in essential oil and citronellol was the major component under all employed treatments. Maximum citronellol/geraniol ratio was obtained at 80 mg.L^-1 nanosilver treatment, indicating the positive influence of nanosilver particles on essential oil quality of Pelargonium plants.