Abstract: Objective: To investigate the effects of different concentrations of ropivacaine on single lung ventilation in thoracic epidural anesthesia.Methods: One hundred and twenty patients with esophageal cancer were randomly divided into the control group,which were treated with simple intravenous anesthesia,and group A,B and C,whose were treated with intravenous anesthesia combined with 0.5%,0.25% and 0.125% of ropivacaine epidural block,respectively(30 cases each group).The mixed venous blood in all patients were analyzed before single lung ventilation and after 15 and 30 min of single lung ventilation.Results: The operation time in group B was shorter than that in group C and control group(P<0.05),the differences of single lung ventilation time between 4 groups were not statistically significant(P>0.05).The fentanyl dosage in A,B and C groups were less than that in control group(P<0.05).The dosage of propofol in group B was less than that in control group(P<0.05),but the differences of which between group A,B and control group were not statistically significant(P>0.05).The SBP and DBP in group A and B were lower than those in control group after 15 and 30 min of single lung ventilation(P<0.05 to P<0.01),the SBP in group C was lower than that in control group after 15 min of lung ventilation(P<0.05),and the DBP in group C was higher than that in group A and B(P<0.05).Conclusions: The different concentrations of ropivacaine in epidural block has different effects on the single lung ventilation,the 0.125% ropivacaine in thoracic epidural anesthesia is safe.