This study aimed to identify the prognostic factors in patients with Waldeyer's ring diffuse large B-cell lymphoma (WR-DLBCL), comparing the efficacy of radiotherapy (RT) for the WR-DLBCL patients in the pre-rituximab and rituximab eras. We conducted a retrospective analysis of 134 patients diagnosed with WR-DLBCL. Univariate and multivariate analyses were performed to identify the prognostic factors for WR-DLBCL. Then, we divided these patients into the rituximab plus chemotherapy group (R-chemotherapy) (n = 88) and chemotherapy group (n = 46), and the Kaplan-Meier and Cox regression model analyses were applied to investigate the treatment value of RT in both the groups. Multivariate analysis revealed international prognostic index (IPI) ≥ 3 and chemotherapy without rituximab as significant risk factors for the progression-free survival (PFS, IPI ≥ 3: p = 0.001; chemotherapy without rituximab: p = 0.002) and overall survival (OS, IPI ≥ 3, p < 0.001; chemotherapy without rituximab, p = 0.024). Rituximab combined with chemotherapy significantly improved PFS (p = 0.002) and OS (p = 0.006) in these patients. RT did not significantly contribute to the survival in the overall cohort analysis, whereas in the subgroup analysis, RT significantly improved the PFS (p = 0.025) and OS (p = 0.029) for the patients in the chemotherapy group, but not in the R-chemotherapy group. In conclusion, the WR-DLBCL patients could benefit from RT in the pre-rituximab era, whereas the addition of rituximab to chemotherapy significantly improved the survival of WR-DLBCL patients, and the clinical benefit of RT was reduced.