Sunflower (Helianthus annuus L.) is largely consumed in Iran as an oleaginous and confectionery product. In this study, the total phenolic and flavonoid contents, antioxidant activity and phenolic composition in different parts of the seeds from six sunflower genotypes were investigated. The antioxidant activity of extract was evaluated by different assays. The total phenolic and flavonoid contents in kernel were 6.8 and 4.1 times higher than those in shell. Antioxidant activity of kernel extract was significantly higher than shell. It can be attributed to higher total phenolic and flavonoid content. In kernel extracts, a positive correlation coefficient was observed between total phenolic content and FRAP (r = 0.636) and Nitric oxide radical inhibition (r= 0. 721) assays. The amount of identified phenolic compounds varied in different extracts and ranged from 0.29 µg/g (Vanillic acid, shell of S5 genotype) to 433.6 µg/g (Syringic acid, kernel of S2 genotype). Therefore, the result indicated that kernel sunflower seeds can be used as potent natural antioxidants in diet.