A 60-year-old male complained of headache, nasal discharge, and diplopia for over one month with a history of left upper molar extraction, and he had recently experienced severe discharge of purulent exudate from his left antrum. Under the diagnosis of maxillary sinusitis, the Caldwell-Luc operation was performed, and several fragments of amorphous white mucoroid materials were removed. In the histological observation, sinus mucosa was relatively well preserved, but showed diffuse infiltration with eosinophilic polymorphonuclears. Huge molds of mucormycosis were associated with the surface of mucosa. He was treated with amphotericin-B deoxycholate, resulting in the uneventful healing of the antral lesion. The current case of antral mucormycosis was very rare but effectively treated by surgical removal of antral mucosa and the following antibiotic therapy for the strong inhabitants of fungal molds. We also presumed that the patient was superinfected with commensal fungus of mucormycosis during broad spectrum antibiotic therapy for the previous dental infection.