The pretreatment albumin/globulin ratio (AGR) has been used as a prognostic factor in various cancers. This study aimed to evaluate the predictive value of AGR in small-cell lung cancer (SCLC).We tested albumin and total proteins in plasma samples from 276 SCLC patients from our cancer center between January 2003 and December 2006. The AGR was defined by the formula: albumin/(total proteins-albumin). The correlation between AGR and overall survival (OS) was examined by Kaplan-Meier and Cox regression methods. For validation, AGR was used to evaluate the prognosis of SCLC in another independent group.Total 276 patients (testing) and 379 patients (validation) were finally enrolled. The median OS was 15.31 months for testing patients and 15.06 months for validation patients, respectively. We determined 1.29 as the cutoff value by using the biostatistical tool (Cutoff Finder), then the patients in the testing group were classified into 2 groups. Kaplan-Meier curves showed high AGR group had significantly longer OS than low AGR group (P = 0.026). According to multivariate analyses, AGR was an independent prognostic factor for OS of SCLC patients in the testing group (HR, 1.35, 95% CI: 1.01-1.81, P = 0.046). In the validation group, AGR was also verified as a predictive factor for OS (P < 0.001), and the risk of SCLC in the low AGR group was 1.43 times higher than that in the high AGR group (HR, 1.43, 95% CI: 1.05-1.94, P = 0.022).AGR is an independent prognostic marker in SCLC patients. Furthermore, it could be of great value in the management of SCLC patients.