Objective To study the dose-response relationship between propofol and isoflurane in balanced anaesthesia. Methods 30 patients, age ranged from 46 to 68 years and body weight from 48 to 72 kilograms, were se-lected. Anaesthesia was induced with propofol 1.5mg/kg,vecuroniura 0.12 mg/kg, fentanyl 2～4μg/kg,and main-rained with vecuronium 1.2μg/kg,fentanyl 2μg/kg. Isoflurane was inhaled at first so that BIS could be maintained on the level of 50～60. Then, minishing the isoflurane concentration by 0.3%～0.5 % and adding the dosage of propofol synchronously, establishing 4～6 balanced level spots of anaesthesia, which could maintain BIS on the level of 50～60 all the time. Recording the isoflurane concentration, the dosage of propofol, MAP, HR, etc, and making the scatterplot graph in virtue of SPSS software. Results The relationship between propofol and isoflurane was accordance with ex-ponential curve model,of which the equation is :y= 102.991 x exp (-1.4456x), R2= 0.784 ; and the ratio of their dosages is 54/1. When isoflurane was inhaled alone at first, MAP was decreased significantly ( P<0.05 ). As the isoflurane concentration minished and the dosage of propofol added, MAP and HR were increasing gradually, but when isoflurane concentration was minished to zero, there is no significant difference as compared with the preanesthesia baseline ( P>0.05 ). Conclusion When BIS was on the balanced level of 50～60, exponential curve relationship ex-ists between the dosage of propofol and isoflurane concentration. If applied reasonabhly, propofol could be good for re-ducing circulation aide-effect of isoflurane.