Recent studies have shown the prognostic nutritional index (PNI) 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, 724 consecutive SCLC patients were included between 2006 and 2013. Demographic, clinical, and laboratory data were collected. The PNI was calculated as 10 × serum albumin value (g/dl) + .005 × peripheral lymphocyte count (per mm(3)). Univariate and multivariate analyses were performed to assess the prognostic value of relevant factors. The optimal cut-off value of PNI for OS stratification was determined to be 52.48. A total of 464 and 260 patients were assigned to low and high PNI groups, respectively. Compared with low PNI, high PNI was associated with older age, advanced stage, and elevated lactate dehydrogenase (LDH). Median overall survival (OS) was worse in the low PNI group (low vs high, 15.90 vs 25.27 months; HR, 0.62; p < 0.001). In multivariate analysis, stage, performance status, LDH, and PNI were independent prognostic factors for OS. Subgroup analysis showed PNI was generally a significant prognostic factor in different clinical situations. The assessment of PNI could assist the identification of patients with poor prognosis and be a hierarchical factor in the future SCLC clinical trials.