Abstract: Polysaccharide was isolated and purified from cactus. The effects of the cactus polysaccharide on removal of reactive oxygen species in some chemical systems were investigated by spectrophotometry. Inhibitory effect of the cactus polysaccharide on the DNA damage induced by hydroxyl radical was investigated by gel electrophoresis. The result demonstrated that the cactus polysaccharide could significantly remove O^₂ and^·OH. This polysaccharide can also efficiently inhibit DNA damage generated by^·OH.