Background: The standard therapeutic regimen for idiopathic chronic eosinophilic pneumonia (ICEP) involves the administration of oral corticosteroids (OCS). However, a notable proportion of individuals experience recurrent episodes after the tapering or cessation of OCS during the course of ICEP. There has been a growing interest in exploring alternative treatment modalities for patients with ICEP at heightened risk of relapse. Objective: The aim of this study was to assess the efficacy of mepolizumab at a dose of 100 mg administered every 4 weeks in preventing relapses of ICEP and its impact on the clinical outcomes. Methods: This retrospective clinical observational study used real-world data to assess the impact of mepolizumab on patients diagnosed with ICEP accompanied by severe asthma. Demographic information and clinical characteristics were extracted from medical records. The study examined the effect of mepolizumab on the annual relapse rate, OCS dose, eosinophil count, and respiratory function parameters. Results: All patients included in the study, with a median (range) follow-up period of 19 months (4-40 months), the annual relapse rate decreased from 0.33 to 0 after the initiation mepolizumab. In addition, the maintenance OCS dose, expressed in methylprednisolone equivalents, declined from 4 mg/day to 0 mg/day. A reduction in the blood eosinophil count was observed, alongside a partial improvement in respiratory function test results among the patients. Conclusıon: A dose regimen of 100 mg of mepolizumab administered every 4 weeks emerges as a promising and well-tolerated therapeutic approach for averting relapses of ICEP.