Abstract: Objective To evaluate the effect of horizontal and trendelenburg left lateral position on the onset time and the spread of intrathecal isobaric bupivacaine for elective cesarean delivery. Methods 180 parturients were enrolled to undergo elective cesarean delivery with combined spinal-epidural anesthesia (CSE). They were randomly divided into 3 groups (n=60) according to the different positions during anesthesia: Group Ⅰ horizontal position, Group Ⅱ trendelenburg position 5°, Group Ⅲ trendelenburg position 10°. A combined spinal-eqidural (CSE) analgesia was performed at the L3-4 interspace in either horizontal or trendelenburg left lateral position, according to randomization. 2 mL of 0.5% isobaric bupivacaine was injected into subarachnoid space when cerebrospinal fluid outflew. Then the patient was placed in a supine position. The success criteria of anesthesia was: T6 sensory block, Bromage grade 2 or 3 (motor block), anesthesia effect ≥gradeⅢ. The systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), sensory block, motor block and adverse reactions such as hypotension, bradycardia, chest distress were observed after the 3 groups parturients entered into operating room. The numbers and success rate of Group Ⅰ, Ⅱ and Ⅲ which got T6 sensory block in ten minutes were observed. Results Among Group Ⅰ, Ⅱ and Ⅲ, there were no significant differences in onset time of sensory block and motor block ( P>0.05). The cold and pinprick sensation level in 10 min of Group Ⅱ and Group Ⅲ were higher than that of Group Ⅰ ( P<0.05). The success rate of Group Ⅱ or Ⅲ was higher than Group Ⅰ ( P<0.05). The success rate of Group Ⅲ was higher than that of Group Ⅱ, but not with significant difference ( P>0.05). There were no significant differences in hemodynamics, adverse reactions such as hypotension, bradycardia, chest distress among three groups ( P>0.05). Conclusion The trendelenburg 5° position can meet the requirement of operation without high anesthesia level.