Abstract: Objective: To compare the effects of different concentrations of levobupivacaine on intercostal nerve block guided by ultrasound.Methods: Ninety patients scheduled by unilateral breast tumor resection were randomly divided into three groups,and anaesthetized at 2 to 5 rib intercostal nerve block guided by ultrasound.The patients were anaesthetized with 24 mL of 0.25% levobupivacaine(group A),16 mL of 0.375% levobupivacaine(group B) and 12 mL of 0.5% levobupivacaine(group C),respectively.The onset time of anesthesia,complete anesthesia time,VAS scores at the beginning of cutting skin and stretching deep tissue,duration of analgesia,and the incidences of incomplete anesthesia and local anesthetic intoxication between three groups were observed.Results: With the increasing of the concentration of levobupivacaine,the onset time of anesthesia and complete anesthesia time shortened,and the analgesia time prolonged in 3 groups(P<0.05 to P<0.01).Conclusions: At the same dosage of levobupivacaine,the appropriate concentration of levobupivacaine at 2 to 5 rib intercostal nerve block anesthesia guided by ultrasound can shorten the anesthesia onset time and complete time,and prolong the analgesia duration.