Objective To investigate the change of N-terminal pro-B-type natriuretic peptide ( NT-proBNP) levels in plasma of patients with stable chronic obstructive pulmonary disease ( COPD) at exertion. Methods Pulmonary function testing, increamental and constant cycle ergometer exercise testing were performed in 19 patients with stable COPD and 10 healthy subjects. Arterial blood gas analysis were measured at rest and maximal exertion in incremental testing. Venous blood samples were drawn both at rest and maximal exercise in constant-load exercise testing and NT-proBNP levels were measured. Results NT-proBNP levels did not change significantly during exercise in the patients with stable COPD[ ( 4803. 86 ±1027. 07 ) ng/L vs ( 4572. 39 ±1243. 33 ) ng /L, P = 0. 542 ] and the control group [ ( 4303. 18 ±771. 74) ng/L vs ( 4475. 71 ±1025. 50) ng /L, P = 0. 676] . NT-proBNP levels were not correlated with parameters of cardiopulmonary exercise testing. Conclusion The factors other than cardiac function may contribute to the exercise intolerance in stable COPD patients without heart failure.