Introduction: Autism Spectrum Disorder is a developmental condition with serious behavioral complications. Although the symptoms and severity vary from person to person, all types of autism affect the ability to communicate with others. Although, there are variety cognitive-behavioral and pharmacologic therapeutic methods, because of complexity of its pathophysiologic mechanisms, many patients suffer from its symptoms during life. So, investigating new treatments is a hot field of research and one of them is using hyperbaric oxygen therapy (HBOT) for autism models in laboratory animals. . .The purpose of this study was to investigate the effect of HBOT on behavioral changes in valproic acid induced autistic rats Methods: 20 male wistar rats were divide in to 2 groups (Saline and VPA). Pregnant rats were injected with normal saline (3.3 ml/kg) as control and 500 mg/kg VPA IP on gestational day 12.5. Rats were undergone behavioral tests (Morris Water Maze, Elevated Plus Maze, Y- Maze, 3 chamber Social Interaction test) at the age of 25 days, autistic rats were exposed to HBOT (2 absolute atmospheric pressure) in a special chamber for 14 days. Each oxygen therapy session lasts 60 minutes. After which, the behavioral tests were performed again. Reasults: In MWM test experimental in comparison to control group showed significantly better performance in finding escape platform. In EPM, HBOT showed anxiolytic effect in experimental rats. In y-maze test repeatitive behaviors significantly were redued in HBOT group. Experimental group of rats showed more significant social interaction with live stimulus in comparison to inanimated objects. Also in this test threated rats performed better social novelty behavior in facing with unfamiliar alive stimuli. Conclusion: Generally, HBOT showed significant therapeutic effect on learning and memory, anxiety, repetitive and social interactions behaviors. Such an effect could be promising method for more future researches in order to find probable molecular mechanisms in reducing oxidative stress and inflammation.

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