Abstract: The present paper deals with the protective effects of Tibetan medical plant Swertia mussotii and its effective constituents——mangiferin and xanthone on liver damage induced by hypoxia.The sterilized water solution of alcoholic extract of S. mussotii (SWSM) was injected intraperitoneally at 6.5 ml/kg/d for 4 days in rats fed at 2,300 m above sea level. The liver weight of the treated rats and its protein, glycogen and total lipid cbntents were almost the same as those of the control group. The activity of SGPT, SGOT, nonsedimentable acid phosphatase and total acid phosphatase of liver tissue did not change appreciably.After rats were exposed to 8,000 m (0.35 atm) for 2 hr, the liver glycogen and protein contents decreased, the total lipid, the SGOT, SGPT and acid phosphatase activity of liver increased significantly. In rats exposed to this altitude, previous injection of SWSM reduced markedly the elevation of SGOT and acid phosphatase activities of injured liver, and reduced the total lipid content, but did not obviously increase the protein and glycogen contents.The assay of hepatic lysosome membrane integrity in vitro indicated that SWSM, mangiferin and xanthone stabilized lysosomal membranes, for they inhibited the release of acid phosphatase. Besides, SWSM, mangiferin and xanthone directly inhibited the activity of lysosomal acid phosphatase in vitro.