Aim To observe changes of pulmonary hypertension and expression of OPN in lung tissue of rat at the state of hypobaric hypoxia at different time and study effect of OPN on pulmonary hypertension. Methods 30 SD rats were divided into 5 groups:Control group(2 260 sea Leval),hypobaric hypoxia (simulate 5000m sea level)1 d,7 d,14 d,21 d group. Mean pulmonary arterial pressure (mPAP),[RV/(LV+S)] of each group were detected. RT-PCR and Western-Blot were used to detect OPN mRNA and protein level in lung tissue of rat. Results mPAP level of hypobaric hypoxia group(1 d,7 d,14 d,21 d) is higher than control group(P<0.05) and increases according to days as 1 d, 7 d, 14 d but decreases in 21 d group(P<0.05). Compared with Control group and 1d group, RV/(LV+S) in hypobaric hypoxia group(7 d, 14 d, 21 d) is higher and higher(P<0.05),but there is no difference between 1d and 7 d group(P>0.05). OPN mRNA,OPN level in lung detected by RT-PCR and Western-Blot of hypobaric hypoxia group(1d, 7d, 14d, 21d) is higher than control group. Conclusion Hypobaric hypoxia increase mPAP and RV/(LV+S) level and expression of OPN. OPN play roles in increasing of pulmonary artery pressure and right ventricular remodeling of high altitude heart disease.