OBJECTIVE: To evaluate the prognostic value of the lymph node ratio(LNR) staging system for rectal cancer following 30 Gy/10 f preoperative radiotherapy. METHODS: Clinical data of 282 patients with mid-lower locally advanced rectal cancer who received preoperative radiotherapy and curative surgery in the Peking University Cancer Hospital from August 2003 to August 2009 were retrospectively reviewed. The radiotherapy regimen was recommended by CACA. Total dose of 30 Gy was divided into 10 fragments (30 Gy/10 f), the biologically equivalent dose (BED) was 36 Gy, and 3D conformal radiotherapy(3D-CRT) was used. Surgery was performed 2-4 weeks after radiation. The prognostic effect of the lymph node ratio(LNR) staging system in addition to the 7th AJCC staging system were retrospectively analyzed and compared in stage III( cases with positive lymph node(s). Patients were divided into four groups by LNR quantiles: LNR1(<0.070), LNR2(0.070-0.142), LNR3(0.143-0.307) and LNR4(>0.307). RESULTS: A total of 108 eligible cases were included in the study. The 3-year disease-free survival (3-yr DFS) was 61.1%. On univariate analysis, circumferential resection margin involvement(P=0.034), tumor differentiation (P=0.002), N stage (P=0.001), TNM stage(P=0.000) and LNR(P=0.003) were significantly associated with 3-yr DFS. On multivariate analysis, abdominoperineal resection (P=0.006, HR=2.611, 95%CI:1.323-5.153), G3-4 differentiation (P=0.015, HR=2.208, 95%CI:1.163-4.192), ypN2a/N2b stage(as covariate: P=0.024, HR=2.568, 95%CI:1.135-5.810; P=0.001, HR=3.759, 95%CI:1.776-7.958) were independent risk factors for decreased 3-yr DFS. Other factors including LNR were excluded in Cox regression model. The 3-yr DFS was statistically different among subcategories of ypN stage. There was no statistical difference of 3-yr DFS in pair-wise comparison of LNR1 and LNR2, LNR2 and LNR3 and LNR3 and LNR4. Additional use of LNR over AJCC staging system did not improve the prediction of prognosis for III(B/C stages and for each stratum of ypN stages, despite the prognostic separation by LNR in III(A stage. CONCLUSION: The LNR staging system in addition to the 7th AJCC staging system does not provide further detailed stratification of the prognosis for stage III( rectal cancer following 30 Gy/10 f preoperative radiotherapy. Lymph node ratio is premature as a prognostic factor in clinical practice.