Abstract: Rosa damascena Mill, (Rosaceae) is a widely cultivated ornamental plant. Several therapeutic effects including calmative, antianxiety, laxative and antispasmodic have been described for the flower of R. damascena. The petals of R. damascena are specially used as cardiotonic by the people of Guilan province. In this study antioxidant potential of R. damascena petals were determined by FRAP test and its ability to inhibit lipid peroxidation was determined by TBARS test in rat. In vivo examination was performed by oral administration of ethanol extract of R. damascena petals at doses of 50, 75, 100 and 200 mg/kg/day for 10 days which compared to vitamin E (10 mg/kg/day) and control groups. In vivo evaluation of antioxidant effects of R. damascene with these two methods showed that the extract of R. damascena has a high ability to inhibit lipid peroxidation and has a high antioxidant power with all doses comparing to control (p<0.001). The highest activity was observed with the dose of 200 mg/kg/day. This preliminary study indicates the interesting anti oxidative stress activity of R. damascena, which is comparable to the known antioxidant compound, alpha-tocopherol. R. damascena can be considered as a medicinal source for the treatment and prevention of many free radicals related diseases.