The main pulmonary artery (PA) to ascending aorta diameter ratio (PA/A) greater than one is a promising indicator of pulmonary hypertension (PH) in acute exacerbation (AE) of chronic obstructive pulmonary disease (COPD) (AECOPD). This study aims to disclose the associations between the PA/A ratio and clinical outcomes in hospitalized patients with AECOPD.Consecutive AECOPD patients admitted to the Department of Respiratory Medicine from September 2017 to July 2021 were reviewed. The treatment success of AECOPD patients was defined as improvement in the clinical condition when discharged from the hospital. Conversely, treatment failure was considered to be an event of in-hospital death or deterioration of the clinical condition prior to discharge.A total of 118 individuals were ultimately reviewed in this study: 74 individuals with a PA/A ratio <1 and 44 individuals with a PA/A ratio ≥1. The outcomes of 21 patients were treatment failure, and 97 patients were considered successes. Patients with a PA/A ratio ≥1 had significantly higher PaCO2, red cell distribution width, brain natriuretic peptide, PA diameters, RICU admission rates, and proportions of treatment failure than patients with PA/A ratios <1 (P < 0.05). The PA diameter and PA/A ratio were significantly increased in the treatment failure group compared with the success group (P < 0.05). A survival analysis indicated that patients with a PA/A ratio ≥1 had worse outcomes than patients with a PA/A ratio <1 during hospitalization (P < 0.05). A multivariate analysis showed that a PA/A ratio ≥1 was an independent risk factor for treatment failure in patients with AECOPD.AECOPD patients with a PA/A ratio ≥1 may have worse outcomes during hospitalization. A PA/A ratio ≥1 may be a promising predictor of treatment failure in patients with AECOPD.