Introduction: Intrathecal fentanyl and dexmedetomidine are adjuvants that can be used along with bupivacaine in spinal anesthesia to enhance the quality and duration of analgesia. Fentanyl is a potent opioid that acts on the muopioid receptors in the spinal cord, which inhibits the transmission of pain signals. Dexmedetomidine is a selective alpha-2 adrenergic agonist that acts on the spinal cord to reduce sympathetic outflow and modulate pain transmission. Material and Methods: 100 ASA I and II patients scheduled for major surgeries under spinal anaesthesia were chosen for the study. Under strict asepsis, using 25 G Quincke spinal needle, lumbar puncture was performed at L 3 - L 4 space. Group F received 3ml, 0.5 % hyperbaric bupivacaine + 25 μg Fentanyl (vol 0.5ml). Group D received 3ml, 0.5 % hyperbaric bupivacaine + 5 μg Dexmedetomidine (vol 0.5 ml). Intra-operatively pulse rate, non-invasive blood pressure, electrocardiogram, SpO2 was recorded. 50 patients in Group F (Fentanyl) and 50 patients in Group D (Dexmedetomidine) were taken to study the changes in haemodynamics and side effects. Chi-square test, Anova test and student' 't' test was done to analyse the data and p value was determined. Results: Dexmedetomidine performed better than Fentanyl as an adjuvant based on the various parameters. Conclusions: Dexmedetomidine is a safe and effective adjuvant for intrathecal administration in the management of postoperative pain as compared to Fentanyl. [ABSTRACT FROM AUTHOR]