Post-operative chemoradiotherapy is one of the therapeutic approaches for operated gastric cancer. During radiotherapy planning, pancreas has not been accepted as a critical organ until now, thus toxicity to pancreas has not been considered. In our prospective study, serum pancreatic enzyme levels and pancreatic volume after RT is investigated. Seventy-one patients with gastric cancer were evaluated adjuvant chemoradiotherapy. Mean pancreas volume, mean pancreas radiotherapy dose and V5, V10, V20 and V40 values were calculated. Fasting blood glucose, insulin, amylase and glycosylated hemoglobin levels were evaluated before radiotherapy and re-evaluated at the end of radiotherapy, at 1th, 3rd, 6th and 12th months after radiotherapy. Pancreas volume was evaluated before radiotherapy and re-evaluated at 12th month after radiotherapy. Before the initiation, after the first session and at the 1th, 3th, 6th and 12th months of radiotherapy, difference between serum Fasting blood glucose (p= 0.179), insulin (p= 0.296), HbA1c (p= 0.468) and amylase levels (p= 0.069) levels were not statistically significant but there is statistically significant decrease in pancreatic volume after treatment (p= 0.002). Postoperative chemoradiotherapy is able to prolong survival and decrease recurrence in operated gastric cancer patients. In our prospective study, we could not identify any statistically significant finding related to pancreatic toxicity or its presentation on biochemical parameters except pancreas atrophy in one-year period. Although, there was not any self-reported diabetes mellitus at early period it, follow-up needed for late toxicity.