Clinical trials have proven the efficacy of therapeutic hypothermia in improving the functional outcome after cardiac arrest (CA) compared with the normothermic controls. Experimental researches also demonstrated quantitative electroencephalogram (qEEG) analysis was associated with the long-term outcome of the therapeutic hypothermia in brain injury. Nevertheless, qEEG has not been able to provide a prediction earlier than 6h after the return of spontaneous circulation (ROSC). In this study, we use CO complexity to analyze the nonlinear characteristic of EEG, which could predict the neurological recovery under therapeutic hypothermia during the early phase after asphyxial cardiac arrest in rats. Twelve Wistar rats were randomly assigned to 9-min asphyxia injury under hypothermia (33°C, n=6) or normothermia (37°C, n=6). Significantly greater CO complexity was found in hypothermic group than that in normothermic group as early as 4h after the ROSC (P<0.05). CO complexity at 4h correlated well with the 72h neurodeficit score (NDS) (Pearson's correlation = 0.882). The results showed that the CO complexity could be an early predictor of the long-term neurological recovery from cardiac arrest.