Objective: To investigate the association between the C-reactive protein/albumin ratio (CAR) and the severity of obstructive sleep apnea syndrome (OSAS). Methods: From January 1, 2012 to December 31, 2019, patients who completed polysomnography in the Department of Otorhinolaryngology, Affiliated Stomatological Hospital of Nanjing University School of Medicine, were collected as research subjects. The severity of OSAS were graded. The distribution of CAR in patients with different severity of disease was evaluated and compared with the clinical data of patients. The logistic regression model was used for multivariate analysis. Results: Two hundred and twenty-three patients were included in final analysis. Of them, 159 patients were male and 64 patients were female with mean age was 49.80±12.83 years (range, 24–69 years). Statistical analysis showed that there was no significant difference in CAR between patients with mild OSAS (P=0.291). The ratio was higher in moderate and severe patients than control group (both P<0.001). The ratio was lower in mild patients than those with moderate and severe degree (both P<0.001). We failed to demonstrate the difference between moderate and severe patients (P=0.496). The receiver operating characteristic (ROC) curve indicated that the cutoff point of CAR was 0.30, and area under curve was 0.849 with a sensitivity of 90.60% and a specificity of 76.49%. Conclusion: Higher CAR may be predictive value for patients with moderate and severe OSAS.