AIM: To investigate the preventive effect of PNS on chronic hypoxic pulmonary hypertension in rats. METHODS: Pulmonary arterial pressure observation, hematocrit (Hct)measurement, biochemical analysis and transmission electron microscopy were conducted to investigate the role of PNS. RESULTS: (1)Mean pulmonary arterial pressure(mPAP), right ventricular mean pressure(RVMP) and Hct were significantly higher in hypoxia group (H group) than that of control group (C group) and were much lower in hypoxia with PNS group (HT group) than that in H group;(2)Nitric oxide (NO 2-/NO 3-) concentration and nitric oxide synthase(NOS) activity in the plasma and the lung tissue, total superoxide dismutase(T-SOD) and copper/zinc-containing enzyme (Cu/ZnSOD) activities in the plasma were all significantly lower in H group than that in C group and were much higher in HT group than that in H group, but NO 2-/NO 3- concentration and NOS activity were still markedly decreased in comparison with C group;(3)Injury of endothelial cells in pulmonary arteriole was improved obviously in HT group compared with H group. CONCLUSIONS: These results suggest that PNS reduces the increase in mPAP, probably through adjusting NO level, anti-damaging effect of free radicals, inhibiting the injury of endothelial cells and decreasing Hct.