Primary stomach lymphoblastic B-cell lymphoma (B-LBL) is a rare tumor. We describe a primary stomach B-LBL in a 38 years old female who presented with nonspecific complaints of fatigue and vomiting for 2 mo.Gastrofiberscopy revealed a large gastric ulcer, which was successfully resected. Pathology showed a lymphoblastic cell lymphoma arising from the stomach, and there was no evidence of disease at any extrastomach site.Immunohistochemical staining and gene rearrangement studies supported that the stomach tumor was a clonal B-cell lymphoma. Therefore, the diagnosis of B-LBL was made based on the stomach specimen.