Marine algae contain large amounts of polysaccharides, which have various biological functions such as antiviral, antitumor and anti-inflammatory activities. However, because of high viscosity of manufacturing, their industrial applications have been limited. Brown algae, one of the marine algae, contain alginic acid, fucoidan, laminarin, mannitol and so on. Alginate is a linear polysaccharide consisting of two uronic acid residues 1,4-linked β-D-mannuronic acid (M) and 1,4-linked α-L-guluronic acid (G). To use alginate efficiently, numerous studies have been conducted about degradation. Alginate degradation using alginate lyases have attracted much attention as biocatalysts and widely used in many applications by preparing functional oligosaccharides from alginate. This study was conducted to investigate the characterization and functionalities of enzymatic extract of Sargassum coreanum (SC) using polysaccharides-degrading enzyme. To obtain the optimum degrading conditions for the SC, the mixture of the SC and crude enzyme from Shewanella oneidensis PKA 1008 was incubated at ratio of 1:1 (v/v) for 0-60 h. The changes in pH, reducing sugar, viscosity, and color of enzymatic extract were measured. The pH value and viscosity were decreased with increasing incubation time. Reducing sugar was increased with increasing incubation time and showed the highest reducing sugar content of 410.07 μg/mL at 60 h. To measure biological activity of enzymatic extract, antioxidant and immune activities were investigated. Enzymatic extract at 48 h showed the highest DPPH radical scavenging activity of 86.36% at 5 mg/mL. Reducing power of enzymatic extract was increased in a concentration-dependent manner at 0-48 h treatment group. The enzymatic extract at 5 mg/mL showed highest lipase and trypsin inhibitory activities of 19.29 and 24.74% at 48 h, respectively. The effects of enzymatic extract on cytokine IFN-γ, IL-2, IL-6, and IL-10 secretion were evaluated. The production of IFN-γ, IL-2, IL-6, and IL-10 by enzymatic extract was increased with increasing incubation time compared to the control. The levels of IFN-γ and IL-2 was the highest values of 93.41 pg/mL and 98.89 pg/mL at 48 h compared to the control (74.90 pg/mL) at concentrations of 100 μg/mL. The production of IL-6 and IL-10 for 48 h at concentrations of 100 μg/mL was 268.45 and 687.36 mg/mL, respectively, which is approximately twice of incubation time at 0 h. These results indicated that crude enzyme from S. oneidensis PKA 1008 can be used to enhance the polysaccharide degradation of SC and incubation time for 48 h was effective to produce alginate oligosaccharide with high antioxidant activities and significant immune activities.