We report herein of a 6-year-old boy with descending necrotizing mediastinitis (DNM) secondary to retropharyngeal abscess, who was successfully treated by the administration of antibiotics. DNM is very rare in children, and surgical drainage of the mediastinum is recommended in adult patients. DNM should be recognized as a severe complication of an oropharyngeal infection in children, and early and accurate diagnosis is important in ensuring appropriate clinical management.