The efficiency of the extract of Persian walnut leaves in stabilizing sunflower oil during oven storage test was studied. The extract of the walnut leaves was prepared with microwave assisted extraction at concentration of methanol 60%. The yield extraction was 32% and the total phenolics were found to be 3704.32±87.60 mg as gallic acid /100g dry leaves. Flavonoids as a part of phenolics were 25.1% of the total phenols (932.2÷3704.32×100=25.1%). The antioxidant activity was measured by reducing ability assay and DPPH radical scavenging assay. Reducing ability assay (EC50 0.143±0.007 mg/ml) and DPPH radical scavenging activity (EC₅₀ 0.080±0.010 mg/ml) revealed that this extract has a high antioxidant activity. Oxidative stability of sunflower oil by walnut leaves was compared with BHA and TBHQ. The results revealed that 320 ppm (0.32 mg/ml) of the Persian walnut leaves extract was comparable with 200 ppm BHA.