Polyporus Umbellatus polysaccharide(PUP) is a new medicine made by our institute. A model of aged mice was prepared by placing 2-month mice in an ozone circumstance (O_3 conoentration 1. 298 ppm) for 10 days. After the aged mice was fed with PUP for 10 days, the average body weight, body temperature and thymus coefficient can be increased to normal level, superoxide dismutase (SOD) activity of red cells and catalase activity of liver were increased, and liver lipoperoxide (LOP) reduced. It is suggested that PUP may be a good anti-aging agent.