A case of orbital abscess with gas gangrene due to odontogenic infection is reported. Although orbital abscesses are rare, they may result in fatal complications. A 68-year-old woman presented with pain and swelling of the left cheek and lower eyelid. She was unable to open her left eye. Oral examination revealed alveolar gingival swelling due to a periapical lesion of the left upper anterior tooth. Computed tomographic scans confirmed abscess formation in the left orbit and the presence of a gas bubble. The ocular tension was 50 mmHg. On admission to our hospital, the patient started to receive antibiotics （PAPM/BP and CLDM）, the left lower eyelid was incised, and the abscess was successfully drained. Alpha-streptococcus, coagulase-negative staphylococcus, and Prevotella melaniogenica were detected in the suppuration. The patient was given a diagnosis of orbital abscess with gas gangrene due to odontogenic infection extending by way of the orbit.