The fungal nasal septum abscess is a rare localized invasive form of fungal rhinosinusitis. Rare cases have been described in the literature. In this article, we intend to describe a new case of fungal nasal septum abscess caused by Aspergillus flavus in diabetic patient after sinonasal surgery. A 53-year-old woman with a history of uncontrolled type 2 diabetes and asthma developed a nasal septum abscess after a sinonasal endoscopic surgery which was performed for nasal polyposis. Needle aspiration of the abscess was performed and the pus cultures were positive for Aspergillus flavus. The patient was treated with antifungal drugs and surgical drainage of the abscess. A clinical and biological improvement was observed. Her case has been followed up for 18 months, and there hasn't been any recurrence of the infection. The fungal nasal septum abscess should be suspected in patients who do not respond adequately to standard treatment of nasal septum abscess, especially patients with risk factors of fungal rhinosinusitis.