Objective To investigate the effect of midazolam as premedication on stress response in patients undergoing cervical plexus block.Methods Sixty female patients undergoing selective thyroid surgery were equally randomized into groups of A and B.The patients in group A were intramuscularly injected midazolam 0.08 mg/kg before cervical plexus block and those in group B were not as the controls.Cervical plexus block was performed with 20 ml mixeture of 1% lidocaine and 0.25% ropivacaine 20 min later.BP and HR were recorded,rate-systolic pressure product (RPP) was calculated,and serum glucose(Glu),cortisol (Cor) and angiotensin Ⅱ (AT-Ⅱ) were detected before enter(T_0),before cervical plexus block(T_1),at 5 min(T_2),15 min(T_3) and 25 min(T_4) after cervical plexus block injection.Results In group B BP,HR,RPP,Glu,Cor and AT-Ⅱ all higher at T_1-T_4 than those at T_0 BP,HR,RPP,Glu,Cor and AT-Ⅱ were all lower in group A than those in group B at T_1-T_4 (P<0.05).Conclusion Intramuscularly premedication with midazolam is effective in reducing stress response in patients undergoing cervical plexus block.