Glycoprotein (GLP) with a molecular mass of ~48 kDa was isolated from Codium decorticatum. Further, characterization of GLP and its potent anti-cancer activities was discussed. GLP is a glycoprotein with 36.24% carbohydrate, composed of rhamnose, galactose, glucose and mannose with a mole ratio of 38:30:26:6. Rhamnose and galactose are thus the main monosaccharides in GLP. FT-IR and NMR spectra proved that GLP contained protein and carbohydrate portions with (1→4)-linked β-galactose residues and β-linked glucose residues. Secondary structure of GLP was estimated using circular dichroism (CD) analysis. Furthermore mass spectrometric analysis was performed for identification of protein using mascot search. The findings of this study serve as a reference for better understanding of the bioactivity of glycoprotein in green algae. Analysis of anticancer potential of this GLP revealed a remarkable inhibition of cell growth in breast, cervical and lung cancer cells.