This study evaluated the antioxidant effects of Rosa damascena (rose) powder on the serum oxidant/antioxidant balance in broiler chickens with cold stress-induced pulmonary hypertension. A total of 192 one-day-old Ross 308 chicks were allocated to four groups: (1) a negative control group fed a basal diet under standard temperature conditions; (2) a positive control group fed a basal diet under cold stress; and (3) rose-0.6% and (4) rose-1.2% groups, which received the basal diet supplemented with 0.6% and 1.2% rose powder, respectively, under cold stress. At 35 days of age, blood samples were collected to measure serum malondialdehyde (MDA) levels and the activities of catalase (CAT) and superoxide dismutase (SOD). Results showed that MDA level was increased in the positive control group compared to the negative control group, while SOD activity was decreased (P<0.05). A significant reduction in serum MDA levels was observed in both rose-supplemented groups relative to the positive control group (P<0.05). Although CAT activity did not differ significantly (P>0.05), SOD activity increased in the 0.6% and 1.2% rose groups compared to the positive control (P<0.05). Furthermore, the right ventricular-to-total ventricular weight (RV/TV) ratio, an indicator of pulmonary hypertension syndrome, was significantly lower in the rose-0.6% supplemented groups (P<0.05). These findings suggest that dietary supplementation with Rosa damascena powder improves the serum oxidant/antioxidant balance and mitigates pulmonary hypertension syndrome in broiler chickens dose-dependently.