Abstract: Objective To examine the effects of high altitude hypoxia on ultrastructure and hypoxia-inducible factor 1α(HIF-1α)expression of lung tissue in the rats with high altitude hypoxia exposure. Methods Forty SD rats were exposed to high altitude hypoxia for 1,2,3,and 30 days,respectively,and a control group(10 rats)was set.The 4 altitude hypoxia groups were transported from the place of 5 m above sea level to the place of 2 700 m above sea level within one hour,to the place of 5 000 m above sea level within 2 hours,and to the place of 4 500 within 3 hours and raised at the place for 30 days. Results Light microscopy and electron microscopy showed that in 2 days acute high altitude hypoxia group there was apparent high altitude pulmonary edema.For the rats with high altitude hypoxia of 30 days,HIF-1α mRNA band integral absorbance values(0.874±0.075)was significantly higher compared with the control group (0.225±0.026,P<0.01)and high-altitude pulmonary edema was significantly reduced. Conclusion Hypoxic acclimatization could increase the expression of hypoxia-inducible factor 1αmRNA and reduce the high altitude pulmonary edema of lung tissue in rats.