The present study was conducted to evaluate the antioxidant activity and nitric oxide synthase (NOS) activation properties of the different extracts of Rhododendron arboreum flower (RaF). Cold water, hot water and ethanolic extract of RaF were evaluated for antioxidant activity against hydroxyl radical, superoxide radical and lipid peroxidation. EC 50 values of cold water, hot water and ethanolic extracts of RaF represented 260, 208 and 41.7 μg/ml respectively in case of hydroxyl radical scavenging activity; 94.7, 154.8 and 36.3 μg/ml respectively in superoxide scavenging activity and 286.3, 239 and 45.6 μg/ml respectively in case of lipid peroxidation inhibition. Ethanolic extract showed significant antioxidant activity in all the test systems. Nitric oxide (NO) production was determined spectrophotometrically by conversion of oxyhemoglobin to methemoglobin. Cold water, hot water and ethanolic extracts also increased significantly nitric oxide production (264, 472.5 and 1041.7 pmol/mg dry wt/h respectively) over the control. Results show that, ethanolic extract possesses maximum antioxidant and nitric oxide synthase (NOS) activation properties, which might be utilized as a promising source of therapeutics.