Granulocytic sarcoma (GS) known as myeloid sarcoma, chloroma, myeloblastoma, or extramedullary myeloid tumor is a neoplasm composed of immature myeloid cells. The common sites of this tumor involvement include bone, central nervous system, soft tissue, lymph nodes, and skin. The involvement of GS in breast tissue is very rare. The incidence of breast GS is 2/1,000,000 in adults. The affected people range in age from 16 to 72. The mean age is 31. Primary, isolate, or non-leukemic GS of breast is defined when bone marrow biopsy confirms the absence of other hematologic malignancy. We here report a case of granulocytic sarcoma of the left breast in a 33 year-old woman who presented with a breast mass. This case was initially diagnosed as diffuse lymphoma, large cell type on H&E histopathology. The tumor cells were, however, strongly positive for myeloperoxidase (MPO), CD117, CD34, and CD43 but negative for CD45, CD20, CD3, or cytokeratin. Although the clinical information such as complete blood count or aspiration biopsy of bone marrow tissue was absent, we finally diagnosed this case as GS by additional immunohistochemical study.