Background: Sensitive-relapsed small-cell lung cancer (SCLC) is thought to be sensitive to chemotherapy; therefore, second-line chemotherapy is recommended. Although platinum rechallenge is performed in the second-line chemotherapy for sensitive-relapsed SCLC, it remains unclear whether such a strategy is effective. Methods: We retrospectively analyzed the outcome of rechallenge chemotherapy for sensitive-relapsed SCLC. The endpoints of this study were progression-free survival from the time of relapse (PFS-Re) and overall survival from the time of relapse (OS-Re). We also compared the toxicity profile of rechallenge chemotherapy to that of first-line chemotherapy. Results: Of the 133 SCLC patients who received first-line treatment, 20 patients satisfied the definition of sensitive relapse and received rechallenge chemotherapy. Combined carboplatin and etoposide was the most commonly used rechallenge regimen, and 17 (85%) received it at a reduced dose due to hematological toxicity during the first-line treatment. Median PFS-Re and OS-Re were 4.5 months (95% CI: 3.5–5.4) and 10.5 months (95% CI: 7.9–13.0), respectively. There was no association between dose adjustment and survival. The frequency of hematologic toxicity tended to be lower with rechallenge than first-line treatment. The incidence of grade 3 febrile neutropenia decreased from 40% in first-line treatment to 15% in rechallenge. Conclusion: Platinum rechallenge could be a useful second-line option for sensitive-relapsed SCLC, having favorable efficacy and safety. Dose adjustment at rechallenge based on the toxicity profile during the first-line chemotherapy could reduce toxicity without weakening efficacy.