Background: To assess the onset time, duration and postoperative analgesic efficacy of ultrasound guided TAP block in children with undescended testis who underwent laparoscopic orcheopexy. Aim of Study: The addition of dexmedetomidine to bupivacaine in TAP block achieves better local anesthesia quality and provides better pain control postoperatively without any major side-effects. Patients and Methods: A prospective randomized controlled double blind study using a computer generated randomization was conducted in Assiut University between March 2016 and September 2017. Results: Regarding SpO 2 and HR of the studied groups at different times; it was noticed that there was no statistically significant differences between the two groups (p>0.05). Regarding end tidal CO 2 measurements, there was a statistically significant difference (p<0.05) after induction, at 10 minutes and at 70 minutes. There was statistically significant difference (p<0.001) after 30-60 minutes and from 80 minutes up to end of surgery with higher mean values at Group A. There was no statistically significant difference at others times. For mean arterial blood pressure recordings, there was statistically significant difference (p>0.001) from time before induction up to after 40 minutes, 80 minutes and at end. There was no statistically significance difference (p>0.05) at time 50-70 minutes, 90 minutes and before extubation. Regarding post-operative pain scores, in Cry, Facial and Torso there was no statistically significant difference at 4 hours, but there was statistically significant difference (p<0.001) at 8 and 12 hours. As regarding child verbal, touch and legs there was a statistically significant difference (p<0.05) at 4, 8 and 12 hours. Regarding frequency of post-operative analgesic request, there was a statistically significant difference between Groups A and B (p<0.05) with (85.0%) request analgesia in Group A vs. (60.0%) in Group B. Egarding the time of the first analgesic request, there was statistically significant difference between Group A and Group B (p<0.001) with higher mean values in Group B than Group A.