Primary breast lymphoma is rare disease which is treated with surgery, radiotherapy and chemoterapy. There is little experience of rituximab treatment is in breast lymphoma. Here we present a case of primary breast lymhoma treated with rituximab and chemotherapy combination. A 58-year-old woman referred for left breast mass. Radiologic imaging showed a mass of 4 cm in diameter. Pathologic examination of excisional biopsy specimen revealed Diffuse Large B Cell Lymphoma with CD20 positivity. The patient was stage IE (Ann Arbor). Mastectomy, lumpectomy or axillary dissection were not performed. Six courses of R-CHOP (CHOP plus rituximab) chemotherapy and radiotherapy were given. The complete response was obtained. The patient has been followed for 36 months with no evidence of disease recurrence. This is one of the first cases treated with rituximab. She has been followed for more than 36 months without relapse.