Background: Acute hypervolemic hemodilution (AHHD) is a common method to save and avoid homologue blood transfusion during surgery. The aim to this study was to evaluate the influence of the hypervolemic hemodilution of hydroxylethyl starch 40 on the EC50 for propofol at two clinical end-points. Methods: We studies 20 patients volunteer undergoing AHHD after epidural anesthesia and 20 patients not receiving hemodilution as a control group. All patients were ASA grade I and aged 20-40 yr and underwent hip arthroplasty surgery. In AHHD group lactated Ringer’s solution 10 ml/kg was infused over 30 min before induction of anesthesia. 20 minutes after receiving 15 ml of ropivcaine 0.5％ epidurally, hydroxylethyl starch 40 (HES 4％) 20 ml/kg was infused within 30 min. In control group the patients received only lactated Ringer’s solution 10 ml/kg. Then propofol was delivered by a Diprifusor target-controlled infusion (TCI). Probit analysis was used to estimate population values for predicted blood and effect-site propofol concentrations at the clinical end-points. Results: in patients undergoing AHHD, the effect-site EC0.5, EC50 and EC95 of propofol were increased by 17％-19 ％(P < 0.05) at the time of loss of consciousness and 11％～16％ (P < 0.05) at the time of recovery of consciousness, respectively, as compared with the patients in control group. Conclusions: We concluded that the patients undergoing AHHD were about 10 ％ less sensitive to propofol than the control. This should be taken into account when propofol is used as hypnotics during AHHD.