The authors have recently observed a case of the Ludwig's angina with forming mediastinal fistula & pneumonia. The Ludwig's angina is a cellulitis of the mouth floor and neck, ie, of the sublingual space. The suppurative inflammation of this space develops from dental infection and can also develop from ulceration or inflammation of the mouth floor, and the tongue base, lingual tonsillitis or salivary calculi. The main causes are characterized as mixed infection with hemolytic streptococcus and staphylococcus are considered to be pathognomic organisms. It may be followed as complications of mediastinal extension, parapharyngeal extension, and laryngeal edema. This is a report on this case with literature review.