and Objectives: Seaweeds are one of the richest sources of natural antioxidants. Antioxidants are main factors of free radical scavenging, which prevent from chronic diseases and food deterioration. These compounds can also be extracted from seaweeds. In this study, the antioxidant activity of the extracts from marine algae Halimeda tuna collected from the coast of Chabahar, was evaluated. Methods: This is an in vitro study. The antioxidant activity of methanol, chloroform, ethyl acetate, and

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... hexanic extracts of the algae, were evaluated using three methods of DPPH, ferrous ion chelating activity, and reduction power methods. Data were analyzed by one-way ANOVA and Tukey test at the probability level of 95%. Results: In this study, the highest antioxidant capacity according to DPPH, was related to the chloroform extract (72.85% inhibition at the concentration of 1mg/ml). In the ferrous ion chelating activity, the highest percentage of chelating was allocated to the methanol extract (81.46%). Based on the data from the reduction power test, the highest reduction activity was related to the methanol extract with absorption of 0.553 (concentration, 1mg/ml). Conclusion: Based on the results of this research, the extracts of Halimeda tuna have the potential for application in medicine and pharmaceutical industry and must be confirmed by preclinical and clinical studies.