The study was conducted with the aim of optimizing and characterizing antioxidant activity of Camellia sinensis and evaluating its preservative effect on Niger seed and Soybean oils. Camellia was prepared by investigating the effect of distilled water concentrations of 100, 150, and 200ml, extraction temperature 80, 85 and 90 ℃ and contact time of 10, 35 and 60 min on its antioxidant activity and extract yield. Based on ANOVA analysis, extraction parameters have significant positive effect (P<0.05) on Camellia antioxidant activity and its extract yield. The best levels of extraction parameters for higher antioxidant activity and extract yield were distilled water concentration of 200ml for 60min at 90 ℃. As DPPH free radical scavenging activity results shown the highest antioxidant activity of Camellia was 96.1%. On the other hand extraction parameters (solvent concentrations, extraction temperature & contact time) were optimized. The best extraction conditions were 200ml, 88 ℃ and 35 min and the results were yield (79.850%) and Antioxidant activity (96.9810%). The preservative effect of Camellia was also studied by performing Free Fatty Acids, Peroxide Value/Acid value on Niger seed and Soybean oils. In the study, all samples were treated with 0, 1 and 2ml levels of Camellia extract and analysis were conducted on weekly basis. Compared to Camellia extract containing Niger seed and Soybean oils, control sample showed higher Free Fatty Acid and Peroxide Values in each storage weeks. Samples treated with 2ml Camellia extract were shown lower Free Fatty Acid and Peroxide Values in each storage weeks. Based on the results, samples with 2ml Camellia extract significantly improved the oxidative stability of Niger seed and Soybean oils. Hence, Camellia has antioxidant activity and preservative effect as evaluated on Niger seed and Soybean oils. Keywords: Antioxidant activity, green tea extract, Camellia sinensis, response surface methodology, DPPH free radical scavenging activity, preservative effect.