Abstract: Objective: To evaluate the clinical effect of small dose of esmolol on the prevention of cardiovasular side effect after cervical plexus block.Methods: Forty patients undergoing thyroid gland operation were randomly divided into control group and esmolol group.The anaesthesia of cervical plexus block was all performed with "single-puncture".The changes of SBP,DBP,HR and SPO 2 were inspected and recorded before anaesthesia and 3 min,5 min,10 min after anaesthesia.The patients in esmolol group were injected 0.5 mg/kg esmolol immedietly after anaesthesia.Results: The difference of each index between the two groups was not significant before operation(P>0.05).The difference of SBP,DBP and HR was marked in the control group before and during anaesthesia(P<0.01);but in the esmolol group,these indexes were relatively calm,especially those of HR,SBP(P>0.05).The difference was significant after anaesthesia between the two groups(P<0.001).Conclusions: Small dose of esmolol can prevent cardiovasular side-effect after cervical plexus block.