To compare the effects of intrathecal dexmedetomidine and intrathecal morphine as supplements to bupivacaine in cesarean sections under spinal anesthesia, full-term parturients (n = 120) undergoing elective cesarean sections under spinal anesthesia were randomly allocated into three groups: Group B received 10 mg bupivacaine, Group BD received 10 mg bupivacaine plus 5 µg dexmedetomidine, and Group BM received 10 mg bupivacaine plus 100 µg morphine. The onset and regression time of sensory and motor blockade, postoperative analgesia, and side effects were recorded. Group BD showed quicker onset time and a longer sensory and motor blockade than other groups (BD vs. B and BD vs. BM, P < 0.05). The mean time of sensory regression to the S1 segment was 253.21 ± 42.79 min in group BD, 192.50 ± 40.62 min in group BM and 188.33 ± 37.62 min in group B (P < 0.001). Group BD showed an analgesia duration (time to requirement of first rescue analgesic) (17.59 ± 6.23 h) similar to that of group BM (16.78 ± 5.90 h) but longer than that of group B (3.53 ± 1.68 h) (P < 0.001). The incidence of pruritus was significantly higher in group BM compared with groups BD and B (P < 0.001). Less shivering was observed in group BD than in groups BM and B (P = 0.009). So intrathecal dexmedetomidine (5 µg) prolonged the motor and sensory blockade, provided a similar analgesic effect and reduced pruritus and shivering compared with morphine (100 µg) in cesarean sections.