The polysaccharide extraction and structural characterization of Codium tomentosum from green algae were investigated in this project. After extraction using acetone and dichloromethane, it was purified with a phosphate buffer to obtain a highly purified Codium tomentosum polysaccharide (CTPS). The structure of CTPS was characterized by high-performance liquid chromatography (HPLC), ultraviolet-visible (UV), Fourier transforms infrared (FTIR), and nuclear magnetic resonance ((HNMR)-H-1) spectrum. Additionally, the DPPH free scavenging activity of CTPS was also examined. Our results determined that purified extract includes L-Arabinose, L-Rammnose, L-Fructose, L-Mannose, L-Galactose, and L-Fucose. Furthermore, it was found that CTPS has free radical scavenging activity. The results showed that the polysaccharide obtained from Codium tomentosum could be applied as a potential natural source.