Microalgae Scenedesmus obliquus was cultivated in nutrient medium either aerated with various levels of CO2 (0.3%, 3%, 9% and 12%) or supplemented with various Fe+3 ions ( 2.5, 5, 10 and 20 mgL-1) in order to accumulation of high amounts lipid and evaluated their chemical composition and bioactivity. Among all algae cultures, biomass yield, total lipid content and lipid productively were significantly differences (P<0.05%), with various degrees of the treated CO2 concentrations, cultures with 12% CO2 exhibited higher lipid content (33.14% of dry weight) and lipid productivity (69.33 mgL-1d-1), with optimum content of fatty acid (FAs) compositions. The major FAs were found to be oleic (18:1, 32.19%), palmitic (16:0, 29.54%) and stearic (18:0, 12.26% of total FAs). Algal cells grown at 20 mg/L Fe3+ concentration had the highest lipid content (28.12%), lipid productivity (94.35 mg/L/d) and FAs profile were C16:0 (25.12%), C18:0 (16.58%) and C18:1 (34.44%).The main antioxidant compounds: total carotenoids, tocopherols and phenolic in algae cells grown at favorite condition (12% CO2 or and 20 mg/L/d) were occurred in significant quantity. The oil obtained from S. obliquus grow at large scale (300 liter, in media aerated with12% CO2 and supplemented with 20 Fe+3 mg/L), showed good antioxidant activity, compared with that of antioxidants standards (a-tocopherol and BHA) as assayed with five antioxidant methods (scavenging radicals of DPPH, ABTS, .OH, superoxide and ferric reducing power). Their antioxidant effect in S. obliquus oil may be correlated with the percent of phenolic, tochopherols and carotenoids. Moreover, the oil showed high proliferation inhibitors action against human breast (MCF-7), hepatic (HepG2) and colon (HCT-116) cancer cell lines, with IC50 values ranged from 11.62 to 15.22 μg ml-1. Thus, S. obliquus oil may serve as sources of natural antioxidants for health promotion and as chemopreventive strategies for various human cancers.