Background: Spinal anesthesia is a widely used technique for lower limb surgeries. The addition of adjuvants like fentanyl and dexmedetomidine to hyperbaric bupivacaine can enhance the quality and duration of analgesia. Objectives: This study aimed to compare the onset and duration of sensory and motor blockade, as well as postoperative analgesia, between intrathecal fentanyl-hyperbaric bupivacaine and intrathecal dexmedetomidine-hyperbaric bupivacaine in patients undergoing lower limb surgeries. Methods: This prospective, double-blind, randomized controlled study included 90 patients undergoing lower limb surgeries under spinal anesthesia. Patients were randomly allocated into three groups: BF (fentanyl-hyperbaric bupivacaine), BD (dexmedetomidine-hyperbaric bupivacaine), and BN (control group). The onset and duration of sensory and motor blockade, as well as postoperative analgesia, were assessed. Results: The results showed that the BD group had a faster onset of sensory block, lower VAS scores, and longer duration of sensory and motor block, as well as postoperative analgesia, compared to the BF and BN groups. Conclusion: Intrathecal dexmedetomidine-hyperbaric bupivacaine provides better analgesic efficacy and longer duration of analgesia compared to intrathecal fentanyl-hyperbaric bupivacaine in patients undergoing lower limb surgeries.