Purpose: Helicobacter pylorurs (HP) is a Gram-negative spiral-shaped microaerophitic bacterium, which colonizes in the gastric mucosa of humans. The gastric human pathogen HP causes chronic gastritis and ulcers, and has a strong relationship with gastric cancer. The aim of this study was to determine advanced oxidation protein products (AOPP) levels, activities of myeloperoxidase (MPO) and catalase (CAT) in two groups. Materials and Methods: For this aim, one group included 30 patients with gastric cancer (Group 1) and the other included 30 subjects with non-gastric cancer and Anti-HP immunoglobulin (Ig) G antibody positive (group 2). Anti-HP IgG antibody test values were found as positive in fifty percent of group I and all of the group 2 patients. Results: Significantly increased AOOP levels were found in group 1 (p < 0.05) compared to group 2. There were no significant differences between the groups in regard to activities of M PO and CAT. In addition, AOPP level, MPO and CAT activities were similar among the Anti-HP IgG positive and negative subgroups of group 1 patients. Conclusion: The result of this study indicated that gastric cancer patients were characterized by increased protein oxidation, whereas there was no significant difference in oxidative stress parameters and antioxidant enzyme activity between the Anti-HP IgG positive and negative gastric cancer patients.