Recent studies have shown that it is not only the absolute number of involved lymph nodes (LNs) but also the ratio of metastatic lymph node that confers prognostic information. However, the impact of the lymph node ratio (LNR) on the prognosis of rectal cancer treated with preoperative radiotherapy is still not fully studied. In this study, Surveillance, Epidemiology, and End Results (SEER)-registered rectal cancer patients treated with preoperative radiotherapy (preop-RT) with LN metastasis were evaluated using multivariate Cox regression analysis to determine the prognostic role of the LNR. LNR optimal cutoff was identified by X-tile. The rationale of yielding pathological node stage (yp-N stage) and yielding pathological lymph node ratio stage (yp-rN stage) (LNR stage) was further combined for analysis. For the results, X-tile program determined 0.28 and 0.68 as optimal cutoff values in terms of survival in 1,872 rectal cancer patients treated with preoperative radiotherapy. yp-rN was significantly associated with 5-year rectal cancer cause-specific survival (RCSS) (P < 0.001). In a multivariate analysis, yp-rN was a significant independent prognostic factor for RCSS (hazard ratios, 1.277 and 1.631; P < 0.001). yp-rN had a prognostic impact on RCSS in patients with yp-N1 and yp-N2 subgroup. yp-N stage also had influenced on RCSS in all yp-rN stage. The yp-rN stage can be used together with the yp-N stage to select high-risk patients for postoperative treatment.