Mucosa-associated lymphoid tissue (MALT) lymphoma is a low grade B cell lymphoma which de velops in MALT. The authors report a case of MALT lymphoma in cecum and ascending colon in a 37-year-old male. He recognized palpable mass and tenderness on right lower abdomen 3 days before admission. At his first admission, he was misdiagnosed as actinomycosis in colon and penicillin G was administered. Four weeks later, he revisited our hospital because of colonic mecha nical obstruction. Subsequently, right hemicolectomy was performed. Macroscopically, infiltrating tumor from terminal ileum to ascending colon was found. Microscopic findings showed glandular mucosa with atypical lymphocytes, lymphoepithelial lesion (LEL) formed by centrocyte-like (CCL) cell invasion of epithelium lining gland, plasmacytoid differentiation and positive B cell marker in immunohistochemical stain. A histological and immunohistochemical study revealed it to be a lowgrade B cell lymphomas of MALT type.