Background: In arthroscopic knee surgery, post-operative pain management is a major concern as spinal anesthesia provides shorter duration of analgesia. Intrathecal opioids as adjuvants are a major help in prolonging the analgesic duration. Aim: To compare the efficacy of intrathecal 0.5% heavy bupivacaine with Dexmedetomidine 5 μg versus Fentanyl 25 μg in patients posted for elective arthroscopic knee surgeries under spinal anaesthesia. Materials and methods: The study was conducted on 80 patients with ASA I and II of either sex aged between 18-60 years. After receiving clearance from ethical committee, the patients were randomly allocated into 2 groups of 40 each. Both the groups received 0.5% hyperbaric bupivacaine 15mg, Group BD received 5µg of dexmedetomidine whereas Group BF received 25µg of fentanyl. Results: Group BD had showed considerably longer sensory and motor blockade time than Group BF. The mean time of sensory regression to S1 was 476±23 min in Group BD and 187±12 min in Group BF. There was no statistically significant difference between the two groups in the beginning of sensory and motor blockade. Conclusions: In arthroscopic knee surgeries, intrathecal dexmedetomidine is associated with extended motor and sensory block, hemodynamic stability, and lower demand for rescue analgesics in 24 hours when compared to fentanyl