Recent cancer researches pay more attention to younger patients due to the variable treatment response among different age groups. Here we investigated the effectiveness of neoadjuvant radiation on the survival of younger and older patients in stage II/III rectal cancer. Data was obtained from Surveillance, Epidemiology, and End Results (SEER) database (n = 12801). Propensity score matching was used to balance baseline covariates according to the status of neoadjuvant radiation. Our results showed that neoadjuvant radiation had better survival benefit (Log-rank P = 3.25e-06) and improved cancer-specific 3-year (87.6%; 95% CI: 86.4-88.7% vs. 84.1%; 95% CI: 82.8-85.3%) and 5-year survival rates (78.1%; 95% CI: 76.2-80.1% vs. 77%; 95% CI: 75.3-78.8%). In older groups (>50), neoadjuvant radiation was associated with survival benefits in stage II (HR: 0.741; 95% CI: 0.599-0.916; P = 5.80e-3) and stage III (HR: 0.656; 95% CI 0.564-0.764; P = 5.26e-08). Interestingly, neoadjuvant radiation did not increase survival rate in younger patients (< = 50) both in stage II (HR: 2.014; 95% CI: 0.9032-4.490; P = 0.087) and stage III (HR: 1.168; 95% CI: 0.829-1.646; P = 0.372). Additionally, neoadjuvant radiation significantly decreased the cancer-specific mortality in older patients, but increased mortality in younger patients. Our results provided new insights on the neoadjuvant radiation in rectal cancer, especially for the younger patients.