Introduction: Painless delivery offers more calmness and collaboration during childbirth, and encourages pregnant women to have vaginal delivery We compared the combined effect of intrathecal sufentanil along with different doses of bupivacaine on the quality and duration of analgesia in painless delivery. Materials and Methods: This clinical trial targeted 40 women (36-40wk) during active labour phase. The subjects were assigned into two groups.and intrathecal injection consisted of sufentanil 5 µg + bupivacaine 1 mg; in the first group and , sufentanil 5µg + bupivacaine 2 mg.in the second group. Both groups were compared in terms of the quality and duration of analgesia, as well as the complications of intrathecal injection. Results: The demographic variables were the same in both groups. Analgesic duration was longer, though insignificant, in the second (bupivacaine 2mg) than first group. The mean pain score and the onset of analgesia were lower in the second group during all times of the study; the difference, however; was not significant There was not any statistically remarkable difference between the 1- and 5-minute Apgar scores, maternal sedation, nausea, vomiting, chills, maximum sensory level and pruritus of both groups. The mean fetal heart rate was lower, though clinically and statistically insignificant, in the high-dose bupivacaine group. Maternal sedation, maximum sensory level and Bromage score did not present any noticeable difference between the first and second groups. Conclusion: According to the results, the 2mg-bupivac group experienced a longer analgesic duration, lower mean pain score, shorter time to analgesia’s onset of action and less complication compared with the 1mg-bupivac group; the difference, nevertheless, was statistically insignificant.