Objective To observe the short-term memory change after dexmedetomidine (Dex) or midazolam(Mid) intravenous infusion．Methods sixty adult patients(ASAⅠ~Ⅱ) were randomly devided into three groups with 20 each,dexmedetomidine group(Group A) , midazolam group (Group B),normal saline group(Group C).In Group A , 0.7μg/kg intravenous Dex was maintained for 10 minutes. In GroupB , 0.07mg/kg intravenous Mid was infusion. In Group C,10ml intravenous NS was given. Every patient watched two different pictures of fruit before and after administration.They were observed for twenty minutes before narcosis.The MAP, HR, SpO2, Bispectral Index (BIS) , AVA/SAI scale, OAA/S scale were monitored. The above parameters were recorded at the time before (T0) and 10 minutes after administration (T1). The memory for pictures were noted when return visit 24h postoperation. Results SPO2 had no different change before and after administration in both two testing groups,while BIS,OAA/S scale,AVA/SAI scale had distinct decreased .Compared with C,the decreasing of BIS,OAA/S scale,AVA/SAI scale were apparent in the two testing groups ( P < 0.05) after administration, which showed an obvious sedative effects of Dex and Mid.All the patients remembered what they had seen in the first picture (T0) (the ratio of recall 100%). Only one patient forgot the second picture in group A(the ratio of forgot 5%),but in group B nobody had rememberd about the second picture(the ratio of forgot 100%). Conclusion For premedication, Dex and Mid provide good sedation effec.Mid caused anterograde amnesia. Dexmedetomidine has minimal impact on memory function,it seemed on amnesia occurrence.