Osteoblastoma is a rare benign bone tumor that occurs unusually in the nasal sinuses. We report one case of sinonasal osteoblastoma in a 12-year-old girl who presented with nasal obstruction and telecanthus on the right side. Computed tomography revealed a lesion of the right ethmoid sinus with heterogenous bony density, which was displacing the orbital contents and the skull base. Biopsy caused significant bleeding. Magnetic resonance imaging showed intense homogeneous enhancement with typical flow-void areas due to large pathological vessels. This MRI feature must alert the clinician on the diagnosis before biopsy and surgical resection after embolization is performed. This case report describes the diagnostic and therapeutic difficulties of this rare tumor.