Abstract: Objective: To observe the effects of the combined administration of propofol and midazolam on PC12 cells impaired by the mimic ischemia and reperfusion（IR）,and to investigate the possible mechanism.Methods: The PC12 cells impaired by IR were grouped as following;the ischemia and reperfusion（IP） group,propofol 12.4μmol·L^-1 group,midazolam(3.3μmol·L^-1,10μmol·L^-1,30μmol·L^-1)groups,propofol 12.4μmol·L^-1 combined with midazolam(3.3μmol·L^-1,10μmol·L^-1,(30 μmol·L^-1)) groups.The degree of impairment was measured by detecting the value of A_570nm.Also the _i was detected of the group IP and those treated by propofol(12.4μmol·L^-1),midazolam(3.3μmol·L^-1,10μmol·L^-1),or both of them.Results: ①Compared with the IP group,the values of A_570nm increased significantly in all groups treated by propofol and midazolam（P＜0.01）.Moreover,the values of A_570nmincreased related to the concentration of midazolam.②The co-administration of propofol and midazolam could further increase the values of A_570nm than which of midazolam and propofol（P＜0.01）.③Compared with IP group,_i was decreased in the other treatment groups（P＜0.01）.And_i of the co-administration groups further decreased than which groups treated with propofol or midazolam alone（P＜0.01）.Conclusion: Both of propofol and midazolam can protect the PC12 cells against the impairment of IP,and the effects can be strengthen when they are administrated at the same time.The mechanism is not clear but at least partially relate to the inhibition of the overload of_i.anesthetics,intravenous;tranquilizing agents;hypoxia-ischemia,brain