Extramedullary plasmacytomas are rare solitary soft tissue tumors that arise from proliferations of malignant transformed monoclonal plasma cell. Though they are closely related to multiple myelomas, they have better prognosis. The tumor is eradicated by surgery or local radiation therapy. This is a case-report study of solitary plasmacytoma tumor which involved left side maxillary sinus and underwent excisional biopsy confirmed by IHC.