Ninety paturients undergoing elective cesarean section were included in this randomized study to compare the influence of the injected volume of epidural morphine (EM) on postoperative analgesia. Three similar groups of patients (n = 30 each) received 2 mg EM in 2 ml, 10 ml, and 20 ml saline respectively one hour after the last dose of 2% lidocaine. Pain scores (0-10) at rest (including uterine contraction pain) at the 2nd, 4th, 8th, 12th, 18th, and 24th h were compared among the three groups. There were no statistically significant differences of pain score among the three groups although lower pain score was present in the 20 ml group since the 8th h and thereafter. Regarding the number of patients who requested additional meperidine for pain relief 3 in 2 ml group, 2 in 10 ml group and 1 in 20 ml group respectively. The result may suggest that the influence of the injected volume of EM on postcesarean analgesia is not obvious.