Introduction: Intrathecal adjuvants can be added to extend the duration of analgesia. To achieve this, several adjuvants, such as the combination of dexmedetomidine with bupivacaine versus fentanyl with bupivacaine, have been used with local anaesthesia during lower limb surgeries. Aim: To compare the combination of dexmedetomidine versus fentanyl with bupivacaine administered intrathecally for the onset and duration of sensory and motor block, as well as their sideeffects and the prolongation of postoperative analgesia in lower limb surgeries. Materials and Methods: A randomised clinical study was conducted on 120 American Society of Anaesthesiologists (ASA) grade I or II patients, aged between 18 and 65 years, who were admitted to the Department of Orthopaedics and General Surgery, Aarupadai Veedu Medical College and Hospital, Puducherry, India for lower limb surgeries under spinal anaesthesia. The patients were randomly assigned to two groups using a computer -generated technique. Group BD received 0.5% bupivacaine (2.5 mL)+10 mcg dexmedetomidine (0.5 mL), while Group BF received 0.5% bupivacaine (2.5 mL)+25 mcg fentanyl (0.5 mL). The onset and duration of sensory and motor blockade, haemodynamic parameters, sedation, and sideeffects of the drugs were analysed. Statistical analysis was performed using Statistical Package for Social Sciences (SPSS) version 2.0 after collecting all the data. Results: There were no statistically significant differences in the subjects' demographics or duration of surgery. However, the duration of sensory block and motor block was significantly prolonged in Group BD compared to Group BF, with values of 720 +/- 32 and 640 +/- 32, respectively. The mean Heart Rates (HR) differed significantly between of the two groups (p-value=0.03). There was no significant difference in sedation scores between the two groups. Group BD showed a higher incidence of bradycardia (n=35) and hypertension (n=32). Conclusion: The combination of dexmedetomidine with bupivacaine, when used intrathecally for lower limb surgeries, demonstrated superior effectiveness in terms of prolonging sensory and motor block duration and providing extended postoperative analgesia, compared to the combination of bupivacaine and fentanyl. However, it is important to note that patients receiving the dexmedetomidine-bupivacaine combination had a higher incidence of bradycardia and hypertension. Therefore, careful monitoring and management of haemodynamic parameters are necessary when using this combination.