Objective To investigate whether patient controlled epidural analgesia(PCEA) with dexmedetomidine(Dex) during cesarean section has no effect on somatosensory evoked potential(SEP) upon lower limb stimulation and serum myelin basic protein(MBP). Methods A total of one hundred and twenty puerperants receiving cesarean section were randomly divided into three groups (n=40): group R received 0.1% ropivacaine only, group RM received 0.002%morphine+0.1% ropivacaine, group RD received 2 μg/kg Dex+0.1% ropivacaine. VAS score, observer's assessment of alertness/sedation(OAA/S) score, HR, MAP were examined 2 h(T1), 4 h(T2),8 h(T3),12 h(T4), 24 h(T5) and 48 h(T6) after surgery. SEPs and concentrations of serum MBP were tested before and after surgery. Adverse effects were also assessed. Results VAS scores at T3, T4, T5 of group RM (1.8±0.8, 1.8±0.8, 1.9±0.9) and RD (1.7±0.6, 1.9±0.7, 1.9±0.5) were lower than those of group R (2.1±0.6, 2.3±0.6, 2.3±0.6)(P 0.05). Satisfaction rates of analgesia and OAA/S scores had no significant difference among three groups (P>0.05). Incidence of nausea, dizziness and pruritus of group RM (32%, 15%, 18%) were higher than those of group R (12%, 0, 0) and group RD (12%, 2%, 2%)(P 0.05). Conclusions Dex 2 μg/kg used for PCEA after cesarean section did not affect serum MBP and SEP, therefore, is a safe analgesic with minimal adverse effect. Key words: Dexmedetomidine; Patient controlld epidural analgesia; Somatosensory evoked potential; Myelin basic protein