Abstract: Objective: To investigate the clinical pathologic characteristics,histogenesis,diagnosis and differential diagnosis of primary diffuse large B-cell lymphoma (DLBCL) of the breast. Methods: Two cases of breast DLBCL were analyzed by immunohistochemistry and morphology,and the related literatures were reviewed. Results: Two patients both noticed a mass in their left breast,and their ages were 46 and 42 years. The tumors were well circumscribed accompanied by the focal region proliferation response of lymphocyte. The tumor cells widespreadly infiltrated in the surrounding tissue. The nucleus of tumor cells were round, irregular and unusual large, accompanied by apoptosis and focal necrosis. Conclusions: Primary DLBCL of the breast,which the tumorgenesis and morphology are similar to lymphoma in other parts,is a rare subtype lymphoma of non-lymph node origin. The recent development of immunohistochemical markers may be useful to distinguish the breast cancer and sarcoma in addition to conventional histological criteria for diagnosis.