Background: The popliteal nerve block is a form of regional anesthesia utilized for a variety of foot and ankle conditions. This form of anesthesia has become a popular technique to decrease postoperative pain, decrease narcotic use, and increase patient satisfaction. Objective: To compare the effect of adding dexamethasone to bupivacaine on duration of sensory and motor blockade of the popliteal sciatic nerve block in below knee surgeries. Patients and Methods: This prospective, randomized, double blinded, control clinical trial was carried out in Aswan University Hospitals for one year on 50 adult patients undergoing surgeries below knee from January 2019 to December 2019. Results: There was no statistically significant difference between the two study groups regarding onset of both sensory and motor blocks, but the durations of both sensory and motor blocks were statistically significantly longer in group A than group B (P=0.001, both). In group A , all the 25 patients (100%) requested their first analgesia through the first 12 hrs postoperatively, While in group B 11 patients (44%) requested their first analgesia through the first 12 hrs postoperatively and 14 patients (56%) requested their first analgesia through the second 12 hrs postoperatively, with statistically significant difference between the 2 study groups (P=0.001). As regard total rescue analgesic dose given (Nalbuphine IV) it was statistically significantly lower in group A than in group B (P=0.001). Conclusion: Addition of dexamethasone to bupivacaine in ultrasound–guided popliteal block significantly prolonged the duration of postoperative sensory and motor block.