A 54-year-old male patient was admitted due to dyspnea with chest pain and reddish swelling in the right lteral neck and right upper which developed 2 or 3 days age. He was treated with acupuncture in the neck about one week ago prior to admission. CT scans of the chest showed density of air and abnormal soft tissue which suggested abscess of the anterior mediastinum and subcutaneous tissue. He underwent cervical and mediastinal drainage with closed thoracostomy and antibiotic therapy. Black-pigmente anaerobic nonspore-forming gram-negative bacilli were isolated from the mediastinal pus and were identified as Prevotella intermedia/nigrescens upon performing biochemical tests and API rapid ID 32A (bioMeriux, France) kit. He underwent decortication of the right side because of loculated empyema on 41st postoperative day. He was fully recovered and discharged on the 82nd hospital day. This was thought to be another case of descending necrotizing mediastinitis not caused by peritonsilar abscess but by cellulitis developed after acupuncture. Early deterction of mediastinits and aggressive drainage of mediastinal abscess are important.