Acute motor axonal neuropathy (AMAN) is a rare immune-mediated disorder characterized by acute flaccid paralysis with elevated levels of GM1 antibodies. It is also known as a subtype of the Guillain-Barre syndrome (GBS) and develops since antigen s serve as antibodies in the spinal cord. We report a case diagnosed as AMAN with symptoms of ascending limb symmetrical weakness. A neurological examination revealed a flaccid paralysis with multiple cranial nerve palsies. Electromyography showed an axonal type of GBS. The patient refused bone marrow fluid aspiration. Intravenous immunoglobulin was administered at the high care unit. Unfortunately, despite the standard therapy, an optimal recovery was not obtained. Hyperbaric oxygen (HBO) therapy has been known to be common in illnesses and some clinical diseases. Although it has not been indicated for peripheral neuropathy, a remarkable recovery was soon visible in the HBO-treated AMAN case. The HBO mechanisms involved here are anti-inflammation and immunomodulation.