Objective To investigate the effects of two different dosages of dexmedetomidine on short-latency somatosensory evoked potentials (SLSEP)in intracranial surgery.Methods Forty pa-tients,ASA Ⅰor Ⅱ,aged 20-65 years old,selected for intracranial surgery were randomly divided in-to two groups,20 patients in each group.Bolus dose of 0.5 μg/kg dexmedetomidine was infused within first 10 min and followed by continuous infusion of 0.5 μg·kg-1·h-1 for 10 min in group A;Bolus dose of 1.0 μg/kg dexmedetomidine was infused within first 10 mins and followed by continu-ous infusion of 1.0 μg·kg-1·h-1 for 10 min in group B.SLSEP indications include N20-P25 amplitute and N20 latent period were observed.MAP,HR,N20-P25 amplitute and N20 latent period were re-corded respectively before dexmedetomidine adminstraition (T0 )and 20 mins after dexmedetomidine adminstraition (T1 ).Results Compared with T0 ,MAP and HR at T1 significantly decreased in both groups(P <0.05).N20-P25 amplitude had no statistically significant difference in both groups,while N20 latent period significantly prolonged (P <0.05).Conclusion Both doses of 0.5 μg/kg and 1.0μg/kg dexmedetomidine can significantly prolong the latent period of N20.