A 51-year-old man had a reddish flat granular lesion in the stomach on endoscopic examination. Histology of biopsied specimen confirmed the diagnosis of low-grade B-cell gastric lymphoma of mucosa-associated lymphoid tissue (gastric MALT lymphoma) and simultaneous infection with Helicobacter pylori. He was given antibiotic treatment. Five weeks later, endoscopy and histology of biopsied specimen showed eradication of H. pylori, and the tumor had regressed. Six months later, H. pylori reemerged, but the tumor had not recurred. After the second antibiotic therapy, H. pylori has been eradicated. The lymphoma has been in remission for 14 months.