Background: Chronic obstructive lung disease is characterized by smoke-related, gradually progressive, fixed airflow obstructions. However, some studies suggested that a reversible bronchial obstruction is common in chronic obstructive lung disease. Such reversibility persists despite the continued treatment with aerosolized bronchodilators and it appears to be related to the diminution in symptoms. The isolated volume response to a bronchodilator is defined as a remarkable increase in the FVC in response to the administration of a bronchodilator whereas the FEV 1 remains unchanged. This has been suggested in patients with severe emphysema. Therefore, the aim of this study was to determine the relationship between the response to a bronchodilator and the severity of an airflow obstruction in COPD patients using the GOLD classification. Methods: This study examined 124 patients with an airway obstruction. The patients underwent spirometry, and the severity of the airflow obstruction was classified by GOLD. The response groups were categorized by an improvement in the FVC or FEV 1 > 12%, and each group was analyzed. Results: Most subjects were men with a mean age of 65.9±8.5 years. The mean smoking history was 41.26±20.1 pack years. The isolated volume response group had relatively low FEV 1 and FVC values compared with the other groups. (p<0.001) Conclusion: In this study, an isolated volume response to a bronchodilator is a characteristic of a severe airway obstruction, which is observed in patient with a relatively poorer baseline lung function.