Abstract: Objective:To explore the edible safety and in vitro antibacterial activity of Sargassum fusifore and its water extract preliminarily. Methods:Analysis of the content of polysaccharides, sulfuric radical, total arsenic and inorganic arsenic in the whole components and the water extract of the Sargassum fusiforme. Study the acute toxicity of the Sargassum fusiforme samples in mice and antibacterial activity in vitro. Results:In group of the whole components, the maximum dose for mice was 12g raw material/kg·BW and equivalent to 120 times the amount of an adult of 50kg intakes each day. In group of the water extract, the maximum dose for mice was 120g raw material/kg·BW and equivalent to 1200 times the amount of an adult of 50kg intakes each day. During observation period, there were no symptoms of poisoning and death phenomenon. The minimum inhibitory concentration (MIC ) of the whole components of the Sargassum fusiforme on Staphylococcus aureus was 125mg/mL and the Minimal bactericidal concentration (MBC) was 250mg/mL. The MIC and MBC of the water extract of the Sargassum fusiforme on Staphylococcus aureus were both 250mg/mL. The Sargassum fusiforme samples showed no obvious bacteriostatic effect on Escherichia coli and Streptococcus mutans. Conclusion: The Sargassum fusiforme samples have a low toxicity, and can both inhibite the growth of Staphylococcus aureus in vitro.