Abstract Background Analgesia is very important after cesarean section because it improves ambulation and enables the mother to give optimal care for the neonate in the immediate postoperative period. Opioids are widely used, but their side effects limit their application. Transversus abdominis plane (TAP) block has been proved to be a useful and safe alternative technique to provide analgesia following abdominal surgeries. Objective to compare the duration of analgesia produced by two drugs fentanyl and dexmedetomidine as adjuvants to bupivacaine in TAP block under ultrasound-guidance after cesarean section in a randomized controlled trial. Patients and Methods In our study, 40 patients were randomly divided into 2 equal groups. The control group received 50 mcg of fentanyl added to bupivacaine on each side. The study group received 50 mcg of dexmedetomidine added to bupivacaine on each side. All patients received equal volumes. Our study showed that addition of a 50 mcg of dexmedetomidine to bupivacaine in ultrasound-guided TAP block has statistically significant effect on the hemodynamic stability of the patients. In addition, dexmedetomidine prolonged the duration of analgesia significantly, as proved by the time of request of first rescue analgesia. Moreover, in dexmedetomidine group, postoperative analgesic requirements were greatly lesser than that of fentanyl group. This makes dexmedetomidine with bupivacaine more superior than the use of fentanyl with bupivacaine. Results In our study, the total rescue analgesia consumed in 24 h postoperatively which was pethidine was less in the TAP-D group (75 ± 25.6 mg) than in the TAP-F group (112.5 ± 42.5 mg). In this study, regarding the measurement the time to the first dose of analgesic received postoperatively, there was a long duration needed in TAP-D group compared to the TAP-F (control group) with the p- value < 0.0001. The time to the first rescue analgesia in the TAP-D group was (659.7 ± 20.99 min.) and for the TAP-F group, it was (512.75 ± 18.1 min.). Conclusion Dexmedetomidine delayed the time to first rescue analgesia when added to bupivacaine in TAP block using ultrasound-guided technique and improved patients’ outcome with decrease in the total pethidine consumption and more hemodynamic stability in comparison to the addition of fentanyl to bupivacaine.