Oilseeds contain different constituents with antioxidant activity especially phenolic compounds and tannins, this study was conducted to evaluate the possible effects of some domestic processes such as dehulling, soaking, ordinary and pressure cooking, germination, fermentation and microwave heating on the contents of phenolic compounds and tannins in some oilseeds. The data revealed that oil seeds could be considered as a rich source of oils and proteins. Phenolic compounds contents of raw oil seeds were; 978.4, 968.0, 862.75, 915.0 and 1063.4 mg/100 g, while, tannin contents were; 510.0, 490.0, 457.0, 457.0 and 440.0 mg/100 g on dry weight basis in peanut, sesame, soybean, safflower and sunflower, respectively. All processing treatments reduced the phenolic compounds except dehulling of sunflower seeds which was increased by 9.6%. Dehulling of oil seeds reduced tannin content by 9-26.5%, while during cooking processes, tannin leaching out in cooking water resulted in a reduction in its content by 4.5-19.6% for ordinary cooking and 5.2-20.2% for pressure cooking. Germination and fermentation processes decreased tannin by 12.5-34.7 and 13.6-49.0%, respectively. Microwave heating treatment had an effect in removal of tannins from seeds than other cooking methods. The reduction ranged between 8.8-24.4% of its initial content in raw oil seeds. The study concluded that all processing treatments used in the study had an effect on the oilseeds content from both phenolic compounds and tannins.