Abstract Postoperative analgesia provides faster rehabilitation, improves patient satisfaction, and reduces hospitalization time. Objective: To compare the analgesic efficacy of two doses of intrathecal morphine (75mcg vs 100mcg) for postoperative analgesia in segmental cesarean sections. Methods: An analytical, experimental, comparative, prospective, random and double-blind study in which the patients were divided into two groups A (75 mcg) and B (100 mcg) administered a mixture of bupivacaine 0.5% 7.5 mg plus morphine in an isobaric to perform a segmental cesarean section. Postoperative Pain (POP) was evaluated through the Visual Analogue Scale (VAS) at 0, 4, 8, 12 and 24 hours. We recorded rescues with NSAIDs and / or parenteral morphine as well as maternal- newborn. Results: in the evaluation of the POP all patients had a similar behavior with p> 0.05. In the rescue with NSAIDs group A merited 41% and in group B 37% with p> 0.5. There were no differences between groups as adverse effects and neonates were born without complications with shut down greater than 7 points at birth and at 5 minutes. Conclusions: intrathecal morphine 75mcg or 100mcg provides the same quality of analgesia with the same incidence of maternal adverse effects and No effects on the neonate. Keywords: segmental Caesarean, intrathecal morphine, postoperative pain.