BACKGROUND Mandibular osteoradionecrosis (ORN) is a devastating complication secondary to the radiotherapy of head and neck cancer. The nutritional status of ORN patients is compromised, but remains rarely studied. We aimed to evaluate the overall nutritional status of patients with ORN and explore the risk factors behind poor nutrition. METHODS This is a single-institution cross-sectional study. Patients diagnosed with ORN were consecutively recruited in a tertiary teaching hospital from July 2017 to August 2019. Multiple laboratory markers and physical indicators were examined to profile their nutritional status. The potential risk factors of poor nutrition were explored by logistic regression. RESULTS A total of 107 patients with ORN were recruited. Among them, almost all patients (95.3%) had at least one laboratory marker lower than the normal physiological range. A total of 40 (37.5%) patients were categorized as undernutrition, who had lower serum albumin (mean difference: 1.8 ± 0.8 g/L; p = .02), prealbumin (mean difference: 26.8 ± 10.8 mg/L; p = .02), and BMI (3.8 ± 0.4 kg/m2 ; p