Abstract: OBJECTIVE To determine the effect of intravenous magnesium sulphate (MgSO4) to bupivacaine-fentanly spinal anesthesia in preeclampsia women undergoing caesarean section. METHODS Sixty women undergoing elective caesarean section were randomly divided into observation group (MgSO₄ group) and the control group. The patients received spinal anesthesia with 7.5 mg hyperbaric bupivacaine and 25 μg fentanyl 15 min after either 20 mL of 0.9% sodium chloride (control group) or 20 mL of 0.05 g·kg^-1 intravenous MgSO₄ (observation group). Combined spinal epidural anesthesia was administered using a standardized technique. The onset and duration of sensory and motor block, duration of spinal anesthesia and postoperative analgesic requirements were studied. Hemodynamic parameters and side effects were recorded, and umbilical arterial blood gases were analyzed and Apgar’s score of neonate were done in both groups. RESULTS The onset of sensory was significantly shorter, and the duration of sensory block, motor block and spinal anesthesia was significantly longer in observation group(P<0.05). yet the onset of motor block was not significantly shorter in observation group. The requirement of postoperative analgesics was significant lower in observation group(P<0.05). Hemodynamic parameters and side effects were similar in both groups. CONCLUSION Intravenous MgSO4 could fasten the onset of sensory, prolong the duration of sensory block, motor block and spinal anesthesia, reduce the consumption of postoperative anesthetics, but not quicken the onset of motor block on bupivacaine-fentanyl spinal anesthesia in preeclampsia women without additional side effects.