Squid ink polysaccharides (SIPS) were isolated from squid ink, a plentiful and multifunctional marine material, and were demonstrated to have amelioratory effects on cyclophosphamide-induced damage in internal organs of model animals by our previous reports. To further investigate the protective effects of SIPS on chemotherapeutic damage caused by cyclophosphamide, this paper evaluated the bioactivities of the marine polysaccharides with a view to their antioxidant ability and their protective effects on deoxyribonucleic acid (DNA) damage using tests such as hydroxyl radicals, reducing power assay and 1,1-Diphenyl-2-picrylhydrazyl (DPPH) radicals, and pEGFP-N1 plasmid DNA treated with ultra violet (UV) plus H2O2. Data revealed that SIPS not only quenched hydroxyl radicals and 1,1-Diphenyl-2-picrylhydrazyl radicals, but showed its strong reducing power and also suppressed oxidative scission on plasmid DNA strand caused by hydroxyl radicals which originated from H2O2shown by UV. Key words: Squid ink polysaccharides (SIPS), antioxidant ability, deoxyribonucleic acid (DNA) damage.