Objective To study the efficacy of hyperbaric oxygen(HO)for the delayed encephalopathy after acute carbon monoxide poisoning(DEACMP)Method One hundred and eleven patients who were diagnozed as the DEACMP from November 2000 to March 2007 in Tangdu Hospital the Fourth Military Medical University were randomly divided into two groups.Thirty-six cases were treated by onventional approach(group A),and 76 cases by HO besides conventional treatment(group B).The efficacy of HO was evaluated after 4courses of treatment. The curative effects were evaluated as(1)cured:clinical symptoms and signs fully disappeared,abnormal electroencephalogram recovered,patients were completely self-help and competent enough for routine work.(2)improved:chnical symptoms and signs partly disappeared,abnormal electroencephalogram partly recovered,patients were partial self-help and incompetent enough for routine work.(3)inefficacy:patient's condition didn't changed.Data were expressed as((x)±s)and analyzed with the chi-quare test and t-test.The statistical significance was established as P＜0.05.Results In group B,62(81.58%)were in good recover,9(11.84%)improved and 5(6.94%)were inefficacy;while in group A:21(58.33%)were in good recover,5(13.89%)were improved and 10(27.78%)were inefficacy.The effciency rate in group B was significantly higher(93.42%)than that(72.22%)in group A(P＜0.05),and the required time for the therapeutic effect noticed time in group B were significantly shorter(P＜0.05)Conclusions HO Can improve the therapeutic effects on DEACMP