Introduction It is important to prevent the development of delayed neuropsychiatric sequelae (DNS) in carbon monoxide (CO) intoxication, but no effective treatment has been clearly identified. Hyperbaric oxygen (HBO) therapy is one of the treatment options in acute CO poisoning; however, whether it can prevent the development of DNS is controversial. The purpose of this study is to compare the effectiveness of normobaric oxygen (NBO) and HBO in preventing DNS. Material & Method This study was conducted on all patients with CO poisoning admitted to the emergency department of a tertiary hospital from 2016 to 2019. We followed up patients to determine whether symptoms of DNS occurred at up to 6 months. We matched the propensity score to an equivalent distribution of potential covariates. Result A total of 224 CO-poisoned patients were enrolled in this study. NBO was used for 26 patients and HBO for 198 patients. DNS occurred in 40 patients. The incidence of DNS was 19.2% in the HBO group, which was higher than the 7.7% observed in the NBO group, but the difference was not significant (p=0.18). After propensity score matching, the incidence of DNS did not differ between the NBO and HBO groups (8.3% vs. 10.4%, p>0.99). Conclusion There was no difference in the incidence of DNS between groups receiving HBO and NBO in acute CO intoxication.