Although nodal invasion represents one of the most powerful prognostic indicators in colorectal cancer (CRC), marked heterogeneity exists within stage III patients. Lymph node ratio (LNR) may offer more precise prognostication in stage III CRC. The aim of this study is to investigate the prognostic impact of LNR on survival in stage III CRC patients. We retrospectively reviewed the data of 288 consecutive patients who underwent radical resection for stage III CRC between January 2000 and December 2008 in the Gastrointestinal Surgery Department, Peking University People's Hospital. The patients were divided into three groups according to LNR quartiles: LNR < 0.167 (n=72), 0.167 ≤ LNR < 0.562 (n = 140), and LNR ≥ 0.562 (n=76). The association between overall survival (OS) and disease-free survival (DFS) and 11 variables including age, gender, tumor location, size, grade, histology, tumor (T) stage, number of metastatic LNs, and LNR was analyzed by multivariate analysis. Survival curves were plotted by the Kaplan-Meier method. Both LNR and the number of metastatic LNs were significant prognostic factors for 5-year DFS and OS in stage III CRC patients. LNR was an independent prognostic factor for 5-year OS. LNR remained an independent prognostic factor in patients with fewer than 12 lymph nodes examined. LNR was a potent independent prognostic predictor for OS and DFS in stage III CRC patients, especially for patients with fewer than 12 lymph nodes examined.