OBJECTIVE To determine the relation between serum myostatin with body mass index (BMI) and PaO₂/PaCO₂ in men with chronic obstructive pulmonary disease (COPD). METHODS A cohort of outpatients with stable COPD was evaluated. We evaluated the myostatin, PaO₂/PaCO₂ and BMI, and the patients were stratified by BMI. The plasma level of myostatin and PaO₂/PaCO₂ was measured by high sensitivity ELISA or blood gas analysis. RESULTS PaCO₂ and myostatin increased significantly compared with those in the control group (P<0.05), but PaO₂ decreased significantly. There was positive correlation between myostatin and PaCO₂ (P<0.05), and negative correlation between myostatin and BMI/FEV1/pred value/PaO₂ (P<0.05). CONCLUSION Patients with higher myostatin levels had a lower BMI, lower PaO₂ and higher PaCO₂, with poor pathogenetic condition and prognosis. Myostatin may be a potential treatment target in patients with chronic obstructive pulmonary disease.