Background: Magnesium sulfate and dexmedetomidine were used as adjuvants to local anesthesia to improve the quality of regional anesthesia. Objectives: To evaluate and compare the effects of magnesium sulfate and dexmedetomidine when added to bupivacaine on the quality of trasversus abdominus plane block (TAPB). Patients and Methods: The study was done at the department of Obstetrics and Gynecology, Faculty of Medicine, Al-Azhar University, Cairo, Egypt from November 2019 to October 2020. A total of 50 female patients undergoing elective Cesarean section using post operative transversus abdominus plane (TAP) block were randomly assigned into two groups; Ultrasound-guided transversus abdominus plane (TAP) block was performed using 20 ml 0.25% Bupivacaine. Magnesium sulfate 150 mg (1.5 ml) and dexmedetomidine 0.5 mcg/kg were added in the magnesium sulfate group and dexmedetomidine group, respectively. Time to first analgesia, pain scores at 2/6/12/24/48 hours, hemodynamic data and side effects were recorded. Results: Dexmedetomidine group provided the longest duration of analgesia and the least consumption of postoperative rescue analgesia versus magnesium sulfate group (P = 0.001). Dexmedetomidine group had higher incidences of bradycardia and hypotension. Conclusion: Magnesium sulfate or dexmedetomidine was a useful adjuvant to bupivacaine for transversus abdominus plane block in lengthening the duration of analgesia. Dexmedetomidine provided quicker onset and longer duration of analgesia with lesser consumption of postoperative rescue analgesia; However, it showed a higher incidence of intraoperative hypotension and bradycardia than magnesium sulfate.