Objective:To investigate the changes of EEG nonlinear properties in unconscious patients and quantify the degree of unconsciousness with EEG nonlinear dynamics analysis. Method:Thirty unconscious patients after severe brain trauma or stroke were involved in the study. All patients' scores with Glasgow Coma Scale (GCS) were below 8. EEG was recorded in all of them under three states: eyes closed, nociceptive stimulus and auditory stimulus. EEG nonlinear indexes such as correlation dimension (D2), approximate entropy (ApEn) and complexity (Cx) were calculated for all subjects. Result: Under eyes closed state, D2, ApEn and Cx nonlinear indexes kept at low level (Correspondingly, 2.84, 0.33 and 0.26). States under nociceptive stimulus and auditory stimulus had no significant difference compared with eyes closed state. Conclusion:With EEG nonlinear dynamics analysis, the degree of suppression of brain cortex in unconscious patients could be directly measured and real-timely monitored. Monitor of EEG nonlinear indexes might be a new technique that could inspect the clinical efficacy of different awaking methods.