Objective To evaluate the effects of a single preoperative dose of gabapentin on buprenorphine patient controlled intravenous analgesia after modified radical mastectorny. Methods Sixty female patients,ASA physical starus Ⅰ and Ⅱ undergoing modified radical mastectomy under general anesthesia were divided into two groups of 30 each group by random digits table to receive either gabapentin 1200 mg (gabapentin group) or a matching placebo (control group), administered orally 2 h before the induction of anesthesia. Subjects received patient controlled intravenous buprenorphi(n)e analgesia during thepostoperative period. Fifty-three patients finished this study, 28 cases in control group,25 cases in gabapentin group. Postoperative pain (static and dynamic),postoperative nausea and vomiting,anxiety,sedation were assessed by pain visual analogue scale(VAS), four-point ordinal scale, anxiety visual analogue scale, Ramsay sedation scale respectively. Postoperative buprenorphine consumption and time to first patient controlled analgesia were observed. Results Postoperative VAS (static and dynamic) was lower in gabapentin group than that in control group (P ＜0.05). Postoperative buprenorphine consumption was (506.1 ±37.9)μg , time to first patient controlled analgesia was (21.1 ±2.3)min,incidence rate of postoperative nausea and vomiting was 40.0% (10/25), antemetic rate was 12.0% (3/25), grade of anxiety was (28.5 ± 12.1) scores in gabapentin group, (699.8 ± 87.8)μ g, (4.3 ±0.8) min,64.3% (18/28),32.1%(9/28) and (66.3±15.7) scores in control group respectively. There were significant differences between two groups (P ＜ 0.05). Conclusion A single preoperative oral dose of gabapentin 1200 mg can effectively attenuate postoperative pain,reduce the consumption of buprenorphine,decrease the incidence rate of postoperative nausea and vomiting,improve patients' anxiety in patients undergoing modified radical mastectomy under general anesthesia.