Osteomyelitis is an infection of bone or bone marrow, caused by pyogenic bacteria or mycobacterium. Osteomyelitis can be acute or chronic, inflammatory process of the bone and its structures. Chronic osteomyelitis will result in variable sclerosis and deformity of the affected bone. With an infection of the bone, the subsequent inflammatory response will elevate this overlying periosteum, leading to a loss of the nourishing vasculature, vascular thrombosis, and bone necrosis, resulting occasionally in formation of sequestra. These become areas that are more resistant to systemic antibiotic therapy due to lack of the normal Havesian canals that are blocked by scar tissue. At this aspect, not only systemic antibiotic therapy, but also surgical debridement maybe required to remove the affected bone and prevent disease propagation to adjacent areas. We experienced a patient who diagnosed tongue cancer and underwent wide partial glossectomy few years before, with an ulcerative lesion around right retromolar trigon. We diagnosed cancer recurrence because PET indicated hot uptake on mandible which was nearby previous tongue tumor site. The patient received hemiglossectomy via paramedian mandibulotomy, partial mandibulectomy and fibula osteocutaneous free flap reconstruction. But final diagnosis was mandible osteomyelitis on pathology report. Here, we present the case with a review of the related literatures.