The present study was designed to investigate the antioxidant potential and oil composition of Callistemon viminalis leaves. GC-MS analysis of the n-hexane extract revealed the presence of 40 compounds. Leaves contained appreciable levels of total phenolic contents (0.27-0.85 GAE mg/g) and total flavonoid contents (2.25-7.96 CE mg/g). DPPH radical scavenging IC₅₀ and % inhibition of linoleic acid peroxidation were found to be in the ranges of 28.4-56.2 μg/ml and 40.1-70.2%, respectively. The haemolytic effect of the plant leaves was found in the range of 1.79-4.95%. The antioxidant activity of extracts was also studied using sunflower oil as an oxidative substrate and found that it stabilized the oil. The correlation between the results of different antioxidant assays and oxidation parameters of oil indicated that leaves' methanolic extract, exhibiting higher TPC and TFC and scavenging power, was also more potent for enhancing the oxidative stability of sunflower oil.