Objective to compare the depth of anesthesia; the effects and side-effects of postoperative analgesia between patients who received intraoperative tramadol both before the start and end of the operation and those who received intraoperative tramadol before the end of the operation. Methods 60 patients undergoing open-abdominal surgery were involved in this study. The patients were randomly divided into 2 groups: patiens received 1.5 mg.kg-1 tramadol both before the start and 30 minutes before the end of the operation (group A) and patiens received 1.5 mg.kg-1 tramadol 30 minutes before the end of the operation (group B). BIS values were recored before and after tramadol administered; anesthesia recovery and VAS values and side-effects of postoperative analgesia were monitered. Results BIS values were comparable before and after tramadol administered in both groups(P>0.05). VAS were significantly lower in group A than in group B during 0.5h～12h after operation(P<0.05 or P<0.01). Ramsay scores, incidence of PONV, dizziness, and supplemental analgesics did not show differences between groups. Conclusion 1.5 mg.kg-1 tramadol administered both before the start and the end of the operation showed better postoperative analgesic effect without increasing side-effects.