Objective: Cancer, one of the major causes of death in the world, is described as a hyperproliferative disorder. Inflammation which is a primary innate immune response to perturbed tissue homeostasis, has become an important hallmark of cancer. Neopterin is produced by activated macrophages upon stimulation with proinflammatory cytokines. It is immune activation biomarker increased in different disorders associated with immune activation, including cancer. We aimed to determine the neopterin levels in gastrointestinal cancers (GIC) and to evaluate the differences among the subgroups. Material and Method:The study included 108 patients with GIC and 25 healthy controls. Patients were divided into three subgroups. The first group consisted of 40 individuals with gastric cancer, the second group consisted of 40 individuals with colorectal cancer, and the third group consisted of 28 individuals with pancreatic, liver or esophageal cancer. Serum neopterin levels were measured by ELISA.Result and Discussion: Neopterin was significantly higher in all patient groups compared to controls (p<0.05). It was found that HDL-cholesterol, albumin and total protein levels were significantly lower in all patient groups compared to controls. Our results show that neopterin levels are elevated in gastrointestinal cancers. Therefore, neopterin may be a potential predictive marker in GIC patients.