Bioactive polymers mainly polysaccharides such as cellulose, chitin, amylose and beta-glucan are well discovered from various sources in nature. Amongst chitin, as the second most abundant polysaccharides after cellulose, is known as a highly insoluble polysaccharide consisting of β-1,4-linked N-acetyl-D-glucosamine, which has been identified as a structural component of crustaceans, crabs, shrimps, insects, and other arthropods, as well as a component of the cell walls of fungi and some alga. Although various bioactive functions are characterized well, less is known about the relationship between structure of biopolymers and their physiological/biological activities. Therefore, more efficient utilization of these raw materials is being required in various fields like in pharmaceutical, medical, agricultural and industrial applications. Since biopolymers are interesting in various applications described above, especially marine alga are of focusing as the plentiful sources for various bioactive compounds including proteins, poly-phenolic compounds, carotenoids and polysaccharides, which was identified as cell wall structural or intercellular components. Structural specificities, substitution patterns and polymerization degrees of polysaccharides are prerequisites of physical and functional properties in alga, even though other biopolymers such as proteoglycans, polymeric phenolics and proteins may participate in the synergic activities and the formation of algal cell wall.