A 21-year-old woman presented to our clinic after 7 years of abdominal pain, diarrhea, and iron-deficiency anemia. Initial upper endoscopy revealed severe inflammation and nodularity of the gastric body and active Helicobacter pylori infection. After eradication therapy, esophagogastroduodenoscopy showed gastric atrophy with nodularity resolution. Histopathology revealed scattered plasma cells, eosinophils, and collagen deposition suggestive of collagenous gastritis. H. pylori can induce proinflammatory cytokines, resulting in fibroblast upregulation. Collagenous gastritis may be caused by an inflammatory response associated with type I, II, and III collagen. Although further research is warranted, we hypothesize that chronic inflammation from H. pylori may lead to collagenous gastritis.