Objective To make comparison of duration of subarachnoid block with intrathecal ropivacaine between gravidas with diabetes mellitus and non-diabetic pregnancy, to evaluate the sensitivity of parturient with diabetes to ropivacaine. Methods 75 parturients who were presenting for elective cesarean section were randomly divided into pregestational diabetes mellitus group (group P, n=15) , gestational diabetes mellitus group (group G, n=30) and non-diabetic parturients group (group N, n=30). After entering the operating room, parturients were given spinal anesthesia spinal at the L3～4 interspace with 0.5％ hyperbaric ropivacaine 3 ml with left lateral decubitus position. To determine the level of sensory block by 10 g monofilament and evaluate the motor block with modified Bromage score. To record the time T6 sensory level was obtained, the onset time of sensory block, motor block, the duration of the motor block and sensory block. Results The time T6 sensory level was obtained of Group P were significantly shortened (P < 0.001). Compared with Group N and Group G, the duration of sensory (P < 0.001) and motor (P < 0.001) block were significantly prolonged. Conclusion Parturients with pregestational diabetes mellitus are more sensitive to 0.5％ hyperbaric ropivacaine compared to non-diabetic parturients. Compared with non-diabetic parturients, there are no difference in the sensitivity of parturient with gestational diabetes mellitus to 0.5％hyperbaric ropivacaine.