OBJECTIVE: To compare the respiratory muscle strength between patients with stable and acutely exacerbated (AE) chronic obstructive pulmonary disease (COPD) at various stages. METHODS: A retrospective medical record review was conducted on patients with COPD from March 2014 to May 2016. Patients were subdivided into COPD stages 1–4 according to the Global Initiative for Chronic Obstructive Lung Disease guidelines: mild, moderate, severe, and very severe. A rehabilitation physician reviewed their medical records and initial assessment, including spirometry, maximum inspiratory pressure (MIP), maximum expiratory pressure (MEP), COPD Assessment Test, and modified Medical Research Council scale. We then compared the initial parameters in patients with a stable condition and those at AE status. RESULTS: The AE group (n=94) had significantly lower MIP (AE, 55.93±20.57; stable, 67.88±24.96; p=0.006) and MIP% (AE, 82.82±27.92; stable, 96.64±30.46; p=0.015) than the stable patient group (n=36). MIP, but not MEP, was proportional to disease severity in patients with AE and stable COPD. CONCLUSION: The strength of the inspiratory muscles may better reflect severity of disease when compared to that of expiratory muscles.