Purpose: This study aimed to identify predictors of lateral lymph node metastasis (LLNM) and assess prognostic factors in patients with locally advanced low rectal cancer (LALRC), with the goal of informing optimal treatment strategies for LALRC. Methods: We retrospectively analyzed clinicopathological data from patients with LALRC who underwent lateral lymph node dissection without preoperative treatment between 2014 and 2023. The radiological criterion for LLNM was a short-axis diameter of ≥6 mm on magnetic resonance imaging (MRI). Results: Of 163 patients, 27 (16.6%) had pathological LLNM (pLLNM). Among 130 patients preoperatively classified as LLNM-negative, 5 (3.8%) were found to have pLLNM. Univariate and multivariate analyses showed that meeting the radiological LLNM criterion independently predicted pLLNM (odds ratio, 53.000; P<0.001). The accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of this criterion were 90.2%, 81.5%, 91.9%, 66.7%, and 96.2%, respectively. In multivariate analyses, pLLNM was an independent risk factor for 3‑year relapse‑free survival. MRI‑detected extramural vascular invasion (mrEMVI) was independently associated with 3‑year relapse‑free survival, local recurrence‑free survival, and distant recurrence‑free survival. Conclusion These radiological criteria may help clinicians develop personalized treatment plans for patients with LALRC. The high negative predictive value and specificity of LLNM assessment can assist in avoiding overtreatment in appropriate patients. Further evaluation is needed to define optimal management for mrEMVI‑positive cases.