Helicobacter heilmannii is a Gram negative, long spiral-shaped organism associated with zoonotic infections acquired from primates including cats and dogs. Infection with H. heilmannii leads to gastritis, peptic ulcer disease, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue (MALT) lymphoma. We experienced a 54-year-old man with dyspepsia who was diagnosed with primary gastric MALT lymphoma (stage IE1) associated with a H. heilmannii-like organism. Upper gastrointestinal endoscopy revealed only microvascular dilatation and mucosal granularity without elevated or ulcerative lesions at the stomach angle. He was probably infected by a pet dog. The man was treated with eradication therapy for 2 weeks including lansoprazole, amoxicillin, and clarithromycin. Four weeks after eradication of the H. heilmannii-like organism, follow-up endoscopy and pathological biopsy findings showed complete remission of the gastric MALT lymphoma. (Korean J Gastrointest Endosc 2011;43:25-29)