This study aimed to investigate the antioxidant potentials of four locally-isolated microalgae. The following four microalgae; Phaedactylium tricornutum, Nannochloropsis gaditana, Nannochloris sp, and Tetraselmis suecica, were screened for their antioxidant activity using DPPH free radical scavenging assay. Natural antioxidants, including carotenoids and phenolics content, were measured in three solvents with different polarities; ethyl acetate, hexane, and water extract biomass. Maximum and minimum concentrations of these compounds were found in Phaedactylium tricornutum and Nannochloropsis gaditana, respectively. Therefore, the total polyphenols and carotenoid content measurement were performed in three solvents extract. The highest antioxidant activity, total polyphenols contents, and carotenoid contents were registered for Phaedactylium tricornutum and Tetraselmis suecica, respectively. The results showed that there is a strong correlation between total polyphenol, carotenoid content, and the total antioxidant activity of the microalgae.