Abstract: Sargassum fusiforme polysaccharides are the most abundant and extremely distinctive ingredients in S. fusiforme. Marine oligosaccharides are products derived from the degradation of marine polysaccharides. To extract more active oligosaccharides from S. fusiforme, we investigated the effects of oligosaccharides on antioxidant and antibacterial properties. We took S. fusiforme polysaccharide through water extraction as the raw material and prepared it by using enzymatic hydrolysis with fucoidan lyase. Then, we conducted single factor and orthogonal trials to optimize the enzymatic hydrolysis process. We examined the average degree of polymerization and reduced sugar content of S. fusiforme oligosaccharides in relation to substrate concentration, enzyme dosage, and enzymatic hydrolysis time. The optimal process parameters for enzymatic hydrolysis of S. fusiforme oligosaccharides were as follows: enzymatic hydrolysis time of 48 h, substrate concentration of 1.5%, enzyme dosage of 20 U·mL⁻¹, and a measured reducing sugar content of (26.53±0.92) mg·mL⁻¹. Thin layer chromatography was used to produce the monosaccharides, disaccharides and trisaccharides. The antioxidant and antibacterial properties of oligosaccharides were determined: when the mass volume concentration was 3.0 mg·mL⁻¹, the scavenging rates of DPPH, ABTS, hydroxyl radical and superoxide anion radical were 63.1%, 80.7%, 71.3% and 57.2%, respectively. When the mass volume concentration was 3.5 mg·mL⁻¹, the reducing power of oligosaccharides was 0.923. The bacteriostatic results show that S. fusiforme oligosaccharides have good bacteriostatic impact on Candida albicans, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. Compared with S. fusiforme polysaccharide, it shows enhanced antioxidant and antibacterial effects.