The characteristics of locked-in syndrome (LIS) are quadriplegia and anarthria with preservation consciousness. It is difficult to manage these symptoms. There have been several reports revealing the significant effectiveness of hyperbaric oxygen (HBO2) therapy on acute stroke, however, some journals show less favorable results using this treatment. There has also been no definite reporting of which lesions of the stroke are suitable for HBO2 therapy. We present a 65-yearold woman, suffered from acute ventral pontine infarction with LIS. Two days after onset, she received HBO2 therapy. One month later, she showed obvious functional recovery. There has been no previous published report discussing HBO2 therapy for acute ischemic pontine infarction. This is the first report regarding the obvious improvements of LIS using HBO2 therapy. Consequently, these findings suggest that HBO2 therapy could be used in conjunction with physical and rehabilitative therapy in the treatment of acute LIS for maximal functional improvement.