The antioxidant activity and the polyphenols and flavonoids contents of methanolic extracts of plant seeds of Canna indica, Hordium sativum and Capsicum annuum were investigated. These extracts were found to exhibit strong scavenging effects on 1, 1-Diphenyl-2-picryle-hydrazyl (DPPH) radicals and have significant amounts of flavonoids and polyphenols. The effects of these extracts on Phosphatidylcholine (PC) liposomes also were studied. It was found that the extractable materials have varying inhibitory effects on oxidation of PC liposomes and their aggregation. These effects were significant and illustrated that addition of these extractable materials to liposomes can enhance their stability by preventing liposome oxidation and aggregation.