Background: Although organizing pneumonia (OP) responds well to corticosteroid therapy, relapse is common during dose reduction or follow-up. Predictors of relapse in OP patients remain to be established. The aim of the present study was to identify factors related to relapse in OP patients. Methods: This study was retrospectively performed in a tertiary referral center. Of 66 OP patients who were improved with or without treatment, 20 (30%) experienced relapse. The clinical and radiologic parameters in the relapse patient group (n=20) were compared to that in the non-relapse group (n=46). Results: Multivariate analysis demonstrated that percent predicted forced vital capacity (FVC), PaO2/FiO2, and serum protein level were significant predictors of relapse in OP patients (odds ratio [OR], 0.82; 95% confidence interval [CI], 0.70-0.97; p=0.018; OR, 1.02; 95% CI, 1.00-1.04; p=0.042; and OR, 0.06; 95% CI, 0.01-0.87; p=0.039, respectively). Conclusion: This study shows that FVC, PaO2/FiO2 and serum protein level at presentation can significantly predict relapse in OP patients.