Most cases of mucosa-associated lymphoid tissue (MALT) lymphoma occur in adults. MALT lymphoma is very rare in children. Helicobacter pylori (H. pylori) infection is known to be an important etiologic factor predisposing to the development of gastric MALT lymphoma. A 12-year-old girl was admitted because of intermittent abdominal pain occurring over the preceding 2 years. Nodular gastritis of the stomach was demonstrated on endoscopy. H. pylori infection was confirmed using the rapid urease test and histopathology. Histopathological examination of gastric biopsy specimens revealed lymphoepithelial lesions pathognomonic of MALT lymphoma, and immunohistochemical staining for CD20 was diffusely positive. Therefore, the patient was diagnosed with gastric MALT lymphoma. Clinical manifestations and histopathologic findings compatible with MALT lymphoma improved with the eradication of H. pylori infection. We report a case of primary gastric MALT lymphoma in a child, associated with H. pylori infection and presenting as nodular gastritis.