Abstract: Objective: To study the clinical and pathological characteristics of breast plasma cell neoplasms as well as the diagnosis and differential diagnosis of it. Methods: Two cases of breast plasma cell neoplasms were analyzed pathologically,and the changes were observed using immunohistochemical method. The related literature was reviewed. Results: One case had primary plasma cell neoplasms on both sides of the breast,and the other was primary breast plasma blastoma. The lump presented no obvious clinical manifestation. Under microscope,most neoplastic plasma cells were similar to normal plasma cells; unusual and untypical tumor cells as well as mitoses were able to be seen. Plasma blastoma displayed proliferating features on large circle cells and ovoid cells which spread widely; vesicular nucleus was in the center of it and nucleolus was obvious; mitoses were easy to see. Two cases showed CD138,CD38,multiple myeloma oncogene-1 and heavy chain IgM. The first case showed light chain κ and the second showed light chain λ. Plasma cell neoplasms showed 20% positive staining for Ki 67, and plasma blastoma showed 70% positive staining for Ki-67. Conclusions: Pathological diagnosis of breast plasma cell neoplasm bases on the tissue shape and immunological manifestation. It must be distinguished from plasma cell mastitis and infiltrating lobular carcinoma. Surgical operation combined with radiotherapy may achieve better treatment results.