Autism is a developmental and behavioral pattern which includes the triad of impairments, 1. social interaction 2. social communication 3. imagination. Inevitable difficulties in the treatment, managing and handle with autistic children are the main problems. Their memories are seemingly in picture or photo records, which are difference from normal population. There are many concepts but no concise in causative factors, including useful treatments, useless and prolong remaining in many studies. HBOT (Hyperbaric Oxygen Therapy) is a quite modern treatment in Thailand for nitrogen imbalance (decompression sickness syndrome or Caisson disease). How can we apply it to treat the autism? A hypothesis shows evidence that neurons surrounding the permanently damaged epicenter of injury can be reactivated with increased oxygen. Oxygen exists in the blood in two forms, combined with hemoglobin and dissolved in plasma. More oxygen is transported by hemoglobin, but oxygen is delivered to the tissues in dissolved form by the liquid portion of blood. HBOT can increase in plasma oxygen to the tissues including the brain. A little change in oxygen can make the better improvements in : cognitive ability, socialization, sleep, calmness, decreased stimming and language. It can make increased in Glutathione (GSH), and Glutathione (GSH) can decreased in oxidative stress with effected to remove metal compounds (mercury) to improve the autism. This clinical trial study divided into 3 group populations 1. general autism 2. post-treatment chiropractic autism 3. medicated autism. This comparative study shows the major clinical symptoms before and after the treatment with HBOT. This study results and analysis are the most important for our further projects planning.