Impaired oxygenation sometimes occurs in patients with acute aortic dissection, however, the mechanism has not been fully investigated. We hypothesized that impaired oxygenation is related to inflammation secondary due to aortic dissection. Patients with acute aortic dissection who had received 14 days of conservative treatment were retrospectively examined. Patients who had undergone surgery or died within 14 days were excluded. Patients who had evidence of having pneumonia or pulmonary congestion during this period were also excluded. Twenty-six patients were divided into a preserved oxygenation group (minimum oxygenation index ≥ 200, n = 13) and an impaired oxygenation group (minimum oxygenation index < 200, n = 13). Maximum serum C-reactive protein (max CRP) and other factors (age, gender, hypertension, diabetes mellitus, smoking, hyperlipidemia, Stanford type, thrombosed false lumen, pleural effusion, atelectasis, use of intravenous vasodilators) for the two groups were compared. Max CRP was the only predictor for impaired oxygenation as calculated by single/multiple logistic regression analysis. Max CRP was significantly higher in the impaired oxygenation group (20.1 ± 2.1 mg/dL) than in the preserved oxygenation group (10.5 ± 1.4 mg/dL, P < 0.05). These results suggest that impaired oxygenation is related to inflammation, which is secondary due to acute aortic dissection.