BACKGROUND: Gastritis was defined as the histological presence of gastric mucosal inflammation. One of the most common aetiology was H. pylori. Gastrin-17 was a hormone that was secreted by G cells. H. pylori infection induced increased in gastrin-17 in gastritis. Therefore, this study was to investigate the relationship of gastrin-17 with gastritis severity and H. pylori infection. AIM: To determine the difference in serum Gastrin-17 level based on gastritis severity and H. pylori infection. METHODS: A cross-sectional study enrolling 45 patients with gastritis was conducted in Haji Adam Malik General Hospital between April and July 2018. Endoscopy and biopsy examinations were performed to confirm the diagnosis of gastritis. Gastritis severity was assessed using the Updated Sydney System. The presence of H. pylori infection was detected by a Campylobacter-like organism (CLO) examination. Gastrin-17 level and demographic data were also gathered. The analysis was done using Mann Whitney and Kruskal-Wallis test. P-value of < 0.05 was considered statistically significant. RESULTS: Serum Gastrin-17 level was significantly different based on gastritis severity (P = 0.001 according to neutrophils infiltration and P = 0.023 according to degree of atrophy), H. pylori infection (P = 0.038), and combined gastritis severity and H. pylori infection (P < 0.001). Serum Gastrin-17 level was higher in subjects with severe neutrophils infiltration, without atrophy, and with H. pylori infection. CONCLUSION: There was a significant difference in serum Gastrin-17 level based on gastritis severity and H. pylori infection.