Background and Aims Gastric cancer is the second leading course of cancer death worldwide and H. pylori infection is an important risk factor for gastric cancer development. This study was design to evaluate the clinical, pathological features, prevalence of H. pylori infection in gastric cancer of Thai patients. Patients and Methods Clinical information, histological features and H. pylori status were collected from gastric cancer patients from Thammasat university hospital and Chulalongkorn university hospital during June 1996-December 2011. H. pylori infection was assessed by histological evaluation, serological test, culture and/or rapid urease test. Clinical information, endoscopic findings and histopathology of all patients were recorded and compared between patients with active or non-active H. pylori infection. Results Total of 100 gastric cancer patients were enrolled in this study. Common presenting symptoms were dyspepsia (70%), weight loss (69%) and anorexia (42%). Mean duration of symptoms prior to diagnosis was 98 days. Overall prevalence of H. pylori infection was 83% and active H. pylori infection was 28%. 1-year and 5-year survival rates were 47% and 0%. There was no difference of mean age, sex, duration of presenting symptom, endoscopic findings and staging between active and non-active H. pylori infection group. Furthermore, there were no significant difference of location (proximal vs non-proximal) and histology (diffuse type vs intestinal type) of gastric cancer between active and non-active H. pylori infection group in this study (25% VS 30%, P-value = 0.1 and 29% VS 29%, P-value = 0.1 respectively) Conclusion Prevalence of H. pylori infection in Thai gastric cancer patients was high but active infection was low. Most of gastric cancer patients presented in advance stage and had grave prognosis. There was no significant difference of clinical information, endoscopic findings and histological type of gastric cancer between active and non-active H. pylori infection in Thailand. Copyright © 2013 American Society for Gastrointestinal Endoscopy. Published by Mosby, Inc. All rights reserved.