Abstract: Ojbective: To evaluate the application of spectral entropy including response entropy（RE） and state entropy（SE） as a new electroencephalographic measure during inducing period of general anaesthesia and compare it with bispectral index（BIS）.Methods: Twenty ASA Ⅰ～Ⅱ patients undergoing elective abdominal surgery were studied.Anaesthesia was induced with propofol,vecuronium and fentanyl iv.After intubation anaesthesia was maintained with propofol infusion and intermittent injection of vecuronium and fentanyl.Applying self-control design,every patient was monitered with spectral entropy and BIS simutaneously.Loss of eyelash reflex together with no responses to verbal commands and slight prodding or shaking were considered to be unconscious,then we recorded the data at following time: baseline values,60s before loss of eyelash reflex、 45s before、 30s before,loss of eyelash reflex、 30s after loss of eyelash reflex、 45s after、 60s after.Results: Prediction probabilities of RE,SE and BIS for loss of consciousness were 0.938 6、 0.931 2 and 0.914 9 respectively,and no statistic differences between them（P＞0.05）;Furthermore,Logistic regressive equations of prediction probability and spectral entropy or BIS were calculated out as ln P_k/（1-P_k）= 20.724-0.267x、 ln P_k/（1-P_k）= 19.278-0.26x and ln P_k/（1-P_k）= 23.865-0.348x respectively.After loss of consciousness,RE and SE kept going down to 23.4±6.5 and 23.9±6.4 and reached the lowest values of 11-18,meanwhile EEG waveform showed suppressed pattern,that meant burst suppression happened.But we couldn't see the similar changes in BIS.Conclusions: Entropy index seems to be better than BIS in predicting loss of consciousness,moreover it can indicate burst suppression.