Abstract: The present disclosure relates to the prevention of osteoporosis and specifically relates to an application of xylan (polyxylose) in the preparation of drugs or food for preventing or treating osteoporosis. The present disclosure proves by utilizing high-purity xylan in animal experimentation that xylan significantly improves bone metabolism, increases blood vitamin D, PINP, and BALP levels, reduces blood CTXI and urine hydroxyproline levels, and reduces urinary calcium loss, thus providing the effects of inhibiting bone resorption and promoting bone formation. Compared with animals having cellulose, lignin, pectin, fructan, glucomannan intakes or having no dietary fiber intake, animals having a xylan intake have higher bone mass and bone density and better bone biomechanical properties. Xylan is suitable for further development into the drugs or food for preventing or treating osteoporosis.