Abstract： Objective To observe the dynamic changes of immune function and prognosis in children with viral encephalitis treated with hyperbaric oxygen (HBO).Methods One hundred children with viral encephalitis were therapied in Yishui Central Hospital in Shangdong province and selected as subjects. They were divided into two groups:HBO treatment group(n=50) and conventional treatment group (n=50). At the same time, healthy control group established (n=50). The changes of symptom, physical sign, electroencephalogram levels of CD4, CD8, CD4/CDS, IgG, IgM and IgA in the two groups before and after treatment were examined. Results Compared with conventional treatment group, the recoveries of symptom, physical sign and EEG were faster (P<0.01 or P<0.05), the patients with sequel such as intermittent headache and impaired memory were fewer (P<0.05) in HBO treatment group. Mter treatment, the levels ofCD4,CD8,CD4/CD8, IgG and IgM were lower (P<0.05)in HBO treatment group than in conventional treatment group and healthy control group. Conclusions HBO can decurtate the course of infantile viral encephalitis and decrease the sequel, but can inhibit infantile immune function obviously.