Inflammatory pseudotumor was originally described in the lung, but recently has been recognized to occur in various sites. A 56-year-old female was referred to our department with a painless swelling of the right midfacial area since 3 months ago. Clinical examination showed non-specific intraoral findings, but asymmetric facial appearance and numbness of the right midfacial area. Plain radiographs and CT images showed aggressive destruction and irregular thickening of the right maxillary sinus wall, increased antral opacification, and destruction of the zygomatic arch. A relatively well-defined soft tissue mass occupied the right maxillary sinus, nasal cavity, zygoma, and infraorbital region. The soft tissue mass showed mild enhancement on CT. Radiographically, this lesion presented a rapidly enlarging mass demonstrating aggressive behavior, mimicking a malignant tumor. Histopathologic examinations showed plasma cells and inflammatory cells in variable fibrotic tissues and demonstrated positive reactivity for vimentin. No malignent changes could be found.