A 63-year-old man hospitalized with COVID-19 developed a serious fungal sinus infection caused by a rare mold called Rhizopus delemar. Despite surgery to remove infected tissue and treatment with antifungal medication amphotericin B, the infection spread and the patient died after five weeks. This was the first documented case of this particular mold causing sinus infection in a COVID-19 patient in Iran, highlighting how severe fungal infections can occur as dangerous complications of COVID-19.