BACKGROUND: Clonidine, alpha2-adrenoreceptor agonist, has nonopiate antinociceptive properties, which might be an alternative for postoperative analgesia free of opioid induced side effects. The aim of this study was to evaluate the fentanyl sparing effect of clonidine and reducing side effects with intravenous administration. METHODS: Fourty seven patients undergoing a cesarean section were randomly allocated to two groups to be given the following agents by intravenous administration. Group I, fentanyl 0.2ng/kg/h with clonidine 0.2ng/kg/h for 72 h adding normal saline for a total of 150 cc. Group II, fentanyl 0.4ng/kg/h for 72 h adding normal saline for a total of 150 cc and analgesia was provided intravenously via patient -controlled analgesia (PCA; basal rate = 2 ml, rescure dose = 1 ml, lock-out time = 10 min). Postoperative analgesia was assessed by VAS at 2, 4, 8, and 24 h after extubation. In addition, we also checked the vital sign sedation score. RESULTS: There were no differences of VAS scores, hemodynamic values except systolic pressure (P < 0.05), or side effects between group I and group II. The frequency of nausea was 8.7% in group I and 29% in group II, and dizziness was 4.3% in group I and 8.3% in group II. CONCLUSIONS: Intravenous clonidine with narcotics is a possible approach to postoperative pain management in patients recovering from major surgery, especially spine surgery, and clonidine spares and reduces side effects in narcotics.