Ten different microalgal species were screened for their antioxidant activity using 2,2´- diphenyl-1-picrylhydrazyl (DPPH) scavenging assay, both total phenolic and carotenoid contents were determined. The ethanolic extract of Oscillatoria sp. showed the highest antioxidant activity (69.1), while the green Chlorella sp. showed higher phenolic content (39.1 mg GAE g-1 dry wt.) and Scenedesmus obliquus recorded higher carotenoid content (3.73 mg L-1), than cyanobacterial species Microalgal biomass plays a great role as a potential source of natural antioxidants, not only due to the carotenoids but also the phenolic compounds. © 2014 Trans Tech Publications, Switzerland.