Pharmacological and biological activities of seaweeds arc significant in terms of human health, functional food and cosmetic applications. One of the most striking properties of seaweeds is their antioxidant activity that protects cells from oxidative damage caused by free radicals that cause many diseases such as cancer, type 2 diabetes, obesity, metabolic disorder, hypertension and cardiac diseases. In this context, evaluation of 1,1-dipheny1-2-picrylhydrazyl (DPPH) radical scavenging activity and ferrous ion chelating activity of methanolic extracts of seaweeds, Cystoseira elegans (Brown algae), Cystoseira amentacea (Brown algae), Padina crassa (Brown algae), Jania rubens (Red algae) and Corallina elongata (Red algae) harvested from Iskenderun Bay, Turkey, were carried out in this study. The total phenolic and total flavonoid contents of the extracts were also determined. According to the obtained results, Cystoseria elegans revealed the best free radical scavenging capacity with the highest flavonoid content and quite high total phenolic content among five seaweed extracts. This study is the first report to examine the antioxidant potentials of Cystoseira elegans and Padina crassa species. As a result of this study, it has been shown that all algae species examined may be potentially rich sources of natural antioxidants.