Pelargonium graveolens L ′Her is an aromatic and medicinal plant which is widely used in pharmaceutical, perfumery and food industry. In this study, the effect of ultraviolet radiation with different intensities (0, 0.12, 0.26 and 0.38 W/m2) was investigated on P. graveolens in InVitro condition. The amount of total phenol, flavonoid and anthocyanin, activity of phenylalanine ammonia lyase (PAL), photosynthetic pigments, carbohydrates, proteins and activity of some anti-oxidant enzymes (Catalase, peroxidase and superoxide dismutase) were evaluated. The antioxidant activity of methanolic extract was measured by using 2-2-di-phenyl-1-picaril hydrazil (DPPH) method. Total protein content and chlorophylls a, b showed a significant decrease (P≤ 0.05), while the amount of carotenoid increased significantly (P≤ 0.05), when ultraviolet radiation increased. With increasing UV-B radiation, the activity of studied enzymes, total phenols, flavonoids and anthocyanins content increased significantly (P≤ 0.05). Also, with increasing radiation intensity, the mean IC50 of methanolic extract decreased. The decreasing pattern of IC50 was consistent with the trend of increasing the mean of phenols. The present results show that P.graveolens in response to UVB stress has increased its antioxidant capacity by increasing the activity of antioxidant enzymes and increasing the phenols.