Petunia ( Petunia hybrida ) an ornamental plant from the Solanaceae family and could be found i three types of bush, creeping and climbing. The low level of rainfall as well as extensive usage of petunia as a green space plant which leads to higher exposure to ultraviolet radiation has negative effects on the morph-physiological characteristics of Petunia. An experiment was performed to investigate the effect of ultraviolet radiation on physiological characteristics and resistance to water stress the Frost fire cultivar of Petunia,. The study was conducted in 1394 to 1395 in the College of Agriculture Isfahan university of Technology greenhouse. The experiment was performed in factorial, randomized complete block design with four levels of UV radiation (No radiation, 10, 20 and 30 KJ/m 2 ) and three levels of drought stress (100%FC, 80%FC and 60%FC) with three replications The results show that the higher levels of UV radiation, the lower in height, besides the increase in the number of stems, flowering stems, flower number, delaying flowering. The investigation of physiological characteristics shows that the imposition of UV-B at 30 kj m -2 and drought stress, reduces chlorophyll, increases phenolic compounds and antioxidant enzymes. An increase in the level of UV radiation and water deficit stress decreases and increases proline respectively. Considering the effects of both UV radiation and water deficit stress, it is obvious that in 80 and 60 percent of field capacity, the intensity of 10 and 20 kJ caused drought tolerance and improved morphological characteristics in plants respectively. The results showed UV-B at 30 kj m -2 led to increase in stem and flower number, flowering stem, deacrease height and chlorophyll concentration, and delay flowering. Keywords: UV radiation, Drought stress, Petunia, Resistance