Background <p>The relationship between regional pathological lymph node status and the benefit of postoperative radiotherapy for gastric cancer remains controversial.</p> Methods <p>This study included all surgically treated patients diagnosed with positive histology and more than 15 examined lymph nodes between January 2007 and December 2019, using data from the SEER database. Patients who received adjuvant chemotherapy were compared by propensity score matching (PSM), with overall survival (OS) as the primary endpoint and adjuvant radiotherapy (RT) as the only variable. Results of subgroup analyses are presented in a forest plot.</p> Results <p>We firstly analyzed the number of patients receiving adjuvant RT and observed a gradual decline from 2000 to 2021. A total of 1882 patients were included from 2007 to 2019, with 1301 (69.1%) in the adjuvant RT group and 581 (30.9%) in the no-adjuvant RT group. After PSM, each group included 573 patients. Overall, adjuvant RT did not significantly improve 3-year OS (55.5% vs. 51.1%, <i>p</i> = 0.07). However, in subgroups of patients with pathologic lymph node metastasis (pN3-stage), aged 55–70 years, with tumor size &gt; 89 mm and T3-stage, adjuvant RT was associated with improved outcome (<i>p</i> &lt; 0.05). Further PSM and survival analysis based on different pathological lymph node stages suggested an association between adjuvant RT and outcomes. Improved survival outcomes were observed in pathologically lymph node positive (pN +) and pN3 groups, but no similar effects were seen in pN1 and pN2 groups. For pN0 patients, although no statistical significance was found, the data suggest that adjuvant RT may not provide additional benefit.</p> Conclusion <p>Adjuvant RT was associated with significantly better prognosis in pN3-stage patients. More researches are needed to further validate the role of adjuvant RT in gastric cancer.</p>