Background Due to the high incidence and mortality of lung cancer, and etoposide is the standard first-line chemotherapy for small cell lung cancer, to evaluate the efficacy and safety of etoposide capsules at different doses as maintenance therapy for patients with extensive-stage small cell lung cancer (ES-SCLC) who show a response to etoposide plus platinum. Methods The study was divided into two stages: stage I, a single-center, one-arm prospective study, and stage II, a multicenter, controlled non-randomized prospective study (patients were chosen from ClinicalTrials.gov Identifier: NCT02179528). All patients received six cycles of etoposide plus platinum. Patients who were evaluated as complete remission (CR) or partial remission (PR) entered the maintenance treatment (MT) (etoposide capsule, once a day for 20 days, every 28 days as a cycle, until disease progression). In stage I, the dose of etoposide was 25 mg; in stage II, patients were non-randomized into etoposide capsule (25 mg/50 mg) and observation groups. In this study, the primary endpoints were progression-free survival (PFS) and safety; the secondary endpoint was overall survival (OS). Toxicity was graded according to the Common Terminology Criteria for Adverse Events v3.0. Results Ninety-two patients were enrolled. In stage I, the median PFS was 6.700 months (95% CI: 6.408–6.992). In stage II, the median PFS of the MT group was better than that in the NMT group (8.930 vs. 5.900 months, P=0.002). In the pooled analysis, the overall median PFS of the MT group was better than that of the NMT group (7.870 vs. 5.900 months, P=0.003). However, there was no significant difference in OS between the groups (15.030 vs. 14.330 months, P=0.813). Multivariate Cox regression analysis showed that maintenance therapy was an independent protective factor for PFS in patients with ES-SCLC. Conclusions Etoposide capsules as maintenance therapy significantly prolonged the PFS of patients with ES-SCLC who responded to etoposide plus platinum, with acceptable tolerability.