Recent studies have shown the combination of C-reactive protein (CRP) and albumin (The modified Glasgow Prognostic Score, mGPS) had prognostic value in some solid tumors. However, no studies have examined its prognostic role in small-cell lung cancer (SCLC) patients. In this retrospective study, 460 consecutive SCLC patients were screened. Eligible patient was assigned a mGPS of 0, 1, or 2 based on pre-treatment plasma CRP and albumin (0: CRP ≤ 10 mg/L; 1: CRP >10 mg/L and albumin ≥ 35 g/L; 2: CRP > 10 mg/L and albumin < 35 g/L). Univariate and multivariate analyses were performed to assess the prognostic value of relevant factors for SCLC. A total of 359 patients were analyzed. The mGPS of 0, 1, and 2 was assigned to 66.3, 30.6, and 3.1 % of total patients. For patients with mGPS of 0, 1, and 2, median overall survival (OS) was 30.4, 28.2, and 14.3 months, respectively (P < 0.001). Performance status (P < 0.001), disease stage (P < 0.001) and pre-treatment LDH (P < 0.001) also significantly predicted OS. Multivariate analyses showed mGPS was an independent prognostic factor (P < 0.001). This study demonstrated that higher mGPS independently predicts worse OS for SCLC patients. The assessment of mGPS could assist the identification of patients with poor prognosis and be a hierarchical factor in the future SCLC clinical trials.