Background: Spinal anaesthesia, a type of regional anaesthesia, is a safe and dependable means of providing anaesthesia as well as appropriate analgesia in infra-umbilical surgery. Intrathecal administration of lipophilic opioids like Fentanyl has proven to enhance spinal anesthesia and provide superior analgesia. This study's objectives were to evaluate the clinical efficacy of intrathecal fentanyl at various doses and assess its negative effects on caesarean delivery patients. Materials and Methods: The current prospective study cohort includes 120 patients, who were further divided into three groups of 40 individuals each. Group A, B and C received 10, 15 and 25 mcg of intrathecal fentanyl. When assessing the clinical efficacy of this study, factors such as the quality of the employed surgical anaesthetic, the onset and duration of the block, the occurrence of any subsequent adverse effects, hemodynamic stability, and the requirement for rescue analgesia were taken into account. Result: A comparative study between the three groups administered with varying dosages of fentanyl indicated that the group receiving the highest dosage (25 mcg) of Fentanyl showed a significantly slower onset of sensory and motor blockage while exhibiting a longer duration of analgesia. in comparison with groups A and B, group C showed a significantly slower onset of sensory and motor blockade while exhibiting a longer duration of analgesia. Intraoperative complications such nausea, Bradycardia, vomiting, and pruritis were seen in 1, 0, 1, and 2 cases in group A, while they were seen in 1, 0, 2, and 2 cases in group B, and in 1, 2, and 5 cases in group C, respectively. The requirement of rescue analgesia was significantly lower in group C as compared to group A and B. Conclusion: For caesarean sections performed under spinal anaesthesia, 15 mcg of intrathecal fentanyl is the ideal dosage to supplement intrathecal hyperbaric bupivacaine