There have been many trials trying to prove the benefit of radiotherapy for gastric cancer; however, the results were either inclusive or controversial. The purpose of the study was to elucidate the effect of radiotherapy on gastric cancer delivered as perioperative or palliative treatment. We conducted systematic searches for trials exploring the effect of radiotherapy on gastric cancer. In the subgroup of patients receiving preoperative radiotherapy for gastric cancer, a significant benefit was found on 10-year overall survival with a hazard ratio (HR) of 0.75 (95% confidence interval (CI), 0.61 to 0.91); however, the benefit on 5-year overall survival was not proven (HR, 0.68; 95%CI, 0.45 to 1.01). There are also no significant differences in resection rate and radical resection rate between group of patients receiving radiotherapy and control group with a relative risk (RR) of 1.06 (95%CI, 0.99 to 1.13) and 1.12 (95%CI 0.93 to 1.36), respectively. In the subgroup of patients receiving postoperative radiotherapy for gastric cancer, survival benefits were found on 3- and 5-year progression-free survival with HR of 0.69 (95%CI, 0.53 to 0.90) and HR of 0.70 (95%CI, 0.61 to 0.80), respectively. Survival benefits of adjuvant radiotherapy on 3- and 5-year progression-free survival were also found; nonetheless, there was no evidence of significant difference in 3-year overall survival (HR, 0.70; 95%CI, 0.61 to 1.01). The effect of radiotherapy on 5-year overall survival was also quite controversial. In short, gastric cancer patients could benefit from radiotherapy both in the form of preoperative radiotherapy and postoperative radiotherapy.