Mucormycosis is a rare opportunistic fungal infection that can implicate cranial sinuses, brain, lungs, gastrointestinal tract and skin. Although it can occur in patients with competent and incompetent immunity such as patients with diabetes mellitus, lymphoma, leukemia and burns, but it has an aggressive, malignant and lethal course in patients with incompetent immunity. To enforce the importance of burn in patients with underlaying diseases such as diabetes, we are going to report a rare case of diabetic burnt patient complicated by right upper extremity myocutaneous mucormycosis. We selected this case to emphasis the importance of underlying disease (diabetes mellitus) with cutaneous burn, aggressive treatment of fungal infection in these patients and referring such case to burn center to prevent catastrophic results. A 50-year-old woman was introduced to us after several days of medical and surgical care of right upper extremity and trunk split-thickness burn. Due to gross muscle necrosis of right upper extremity and poor general condition of the patient, she was taken to the operating room that led to right upper extremity amputation and several times of aggressive debridement to save her life. Pathologic report was indicative of mucormycosis. We can conclude from this case that: 1) Burn, even partially thickness and with little body surface area, should be referred to burn center for better care 2) No response to usual medical treatment should make us more sensitive to consider the unusual causes of infection such as fungi 3) Suspected dead tissues should be excised aggressively especially if suspiciousness to wound sepsis and fungal infection is present especially in an immunocompromised patient.