Objective To investigate the value of electroencephalogram (EEG) nonlinear parameters in assessing the therapeutic efficacy in patients with acute carbon monoxide poisoning (ACMP). Methods Twenty-one patients diagnosed with ACMP in our department from November 2010 to March 2011 and 21 healthy volunteers were enrolled in this study.The EEG nonlinear parameters were obtained fi om the patients for analysis on the day of admission, at 2 and 4 weeks post-treatment,respectively,including approximate entropy (ApEn),cross-approximate entropy (C-ApEn),correlation dimension (D2),point wise correlation dimension (PD2),mutual dimension (Dm),Lyapunov exponent (LE),Kolmogorov entropy (KE) and Complexity (Cx).The EEG nonlinear parameters of the patients were compared with those of the healthy volunteers. Results The mean values of D2, Cx,ApEn,C-ApEn and Dm were found to gradually increase with the duration of therapy, whereas the values of PD2,LE and KE had no association with the therapy.On the day of admission,the mean values of D2,Cx,ApEn, C-ApEn and Dm for ACMP patients were significantly different from those of the healthy volunteers (P＜0.05),but at 2 and 4 weeks post-therapy,the mean values ofLE,PD2,D2,Dm,Cx,ApEn and C-ApEn of the ACMP patients were not significantly different from those of the healthy volunteers (P＞0.05). Conclusion Since EEG nonlinear parameters (D2,DM,Cx,ApEn,C-ApEn) can objectively reflect the status of brain functional recovery in ACMP patients at an early treatment stage,they can serve as practical measures in the treatment of ACMP.