摘要Objective: To evaluate the in vitro antioxidant activity of Sargassum wightii (S. wightii) andUlva lactuca (U. lactuca). Methods: Dried seaweeds of S. wightii and U. lactuca were tested for total phenolic content. In vitro antioxidant activity was determined by DPPH assay and ferric reducing antioxidant power (FRAP) assay. Functional groups of two seaweeds were analysed by fourier transform infrared spectroscopy (FTIR). Results: The highest total phenolic content was observed in S. wightii (0.65±0.02 mg GAE/g) when compared with U. lactuca. In vitro antioxidant activity of S. wightii showed higher activity in all assays than U. lactuca with the higher total antioxidant activity (123.40±4.00 mg ascorbic acid/g), DPPH radical scavenging activity (108.06±1.02)% and ferric reducing antioxidant power (153.40±1.41 mg GAE/g). FITR spectrum of standard gallic acid was compared with seaweeds and same number of peaks lying between 449.32 and 3 495.89 cm-1 and 462.89 and 3 407.05 cm-1 was recorded. Conclusions: These results show that S. wightii has higher antioxidant capacity than U. lactuca. Further study is necessary to exploit the multifunctional properties of seaweeds which will be usefull to treat many diseases.