Background: Caudal block is one of the most common regional anesthetic techniques used in children. It is considered safe and simple procedure but its main disadvantage is its relatively short duration of action even with use of long acting agents such as bupivacaine.Fentanyl is most common additive to local anesthetics to caudalblock, but it has undesirable side effects. Dexmedetomidine is α₂ adrenergic receptor agonist which prolongs the duration of analgesia when added to caudal bupivacaine. Objective: This work aimed to compare the postoperative analgesic and any side effects of addition of either dexmedetomidine or fentanyl to bupivacaine in pediatric patients undergoing lower abdominal and lower limb surgeries. Patients and methods: This interventional randomized-controlled study was carried out in Department of Anesthesia and Intensive Care, Sohag University Hospital. Sixty patients aged from 2 to 6 years who were going to do a lower abdominal surgery were included in the study. Results: As regards sedation score, dexmetedomidine showed more sedation than that of fentanyl where there was a significant difference between both groups at ½ hour and 1 hour (P value 0.008 and 0.016respectively) and number of children sedated in group D (23) was more than that of group F (8) at 1 hour. Conclusion: Adding dexmetedomidine to bupivacaine in caudal block is longer in duration of postoperative analgesia and showed more sedation time than that of fentanyl with more stability in haemodynamics.