Aim To study the effects and mechanism aroused from inhalation of nitric oxide (NO) in patients with chronic obstructive pulmonary disease (COPD) and pulmonary hypertension (PH). Methods The pulmonary and systemic hemodynamics, blood gas exchange, oxygen transportation, guanosine 3', 5'-cyclic monophosphate (cGMP), and methemoglobin (MetHb) level were measured with Swan-Ganz catheter in 18 patients with COPD-PH before and after inhalation of 40 ppm NO. Results The pulmonary vascular resistance (PVR) was decreased by 28.1%, 31.3% and 34.4%, respectively, meanwhile the mean pulmonary arterial pressure (mPAP) was also decreased after continuous inhalation of NO for 2 min, 8 min and 15 min (P<0.01). Both mPAP and PVR were returned to basic line in 2 min after a stop of inhaled NO. Moreover, few effects of inhaled NO on systemic arterial pressure and systemic vascular resistance was observed. After inhaled NO 15 min, PaO 2 was increased from 6.9±1.5 kPa to 7.8±1.9 kPa, Qs/Qt was decreased from 26%±6% to 20%±7% , and mixed venous cGMP level was increased from 14.6±7.8 pmol/L to 28.9±6.7 pmol/L (P<0.05), but VA/Q, arterial oxygen transport, coefficient of oxygen delivery, and MetHb level were not altered during inhalation of NO. Conclusion The data indicate that the pulmonary blood vessel in COPD-PH can be dilated immediately and selectively, gas exchange in lung can be improved during inhalation of NO , the mechanism of which may be related to increase of cGMP.