Descending necrotizing mediastinitis (DNM) is a rare but severe disease with a high mortality rate. We report a case of a 77-year-old woman with DNM who was treated using video-thoracoscopic drainage and a Blake drain. She was admitted to our hospital with a 3-day history of a sore throat. Computed tomography (CT) revealed a peritonsillar abscess descending into the anterior and posterior mediastinum below the carina. She was diagnosed with DNM, and emergency surgery was performed. The mediastinal abscess was drained via video-thoracoscopy, and a 24F Blake drain was inserted into the mediastinum. Following mediastinal drainage, cervical drainage was performed for treatment of the retropharyngeal abscess. The outcome of videothoracoscopic mediastinal drainage was satisfactory, and no further invasive treatment was required. We believe that video-thoracoscopic mediastinal drainage is an effective, minimally invasive treatment for DNM with subcarinal spread. Blake drains are useful for mediastinal drainage.