Spinal anaesthesia is preferred regional anaesthesia technique in lower abdominal surgeries. Advantages are conscious and spontaneously breathing patient [25], good muscle relaxation, cost effectiveness and adjuvants injected intrathecally prolong the anaesthetic effects [26,27]. Aim of the study: To compare Fentanyl Citrate and Magnesium sulfate as adjuvants to 3 ml of 0.5% bupivacaine in infraumbilical surgeries under spinal anaesthesia, about onset and duration of sensory and motor block, intraoperative hemodynamics, postoperative pain and side effects. Materials & Methods: After Institutional ethics committee approval, a double-blinded comparative study was conducted in 100 patients at Osmania General hospital during 2014-2017. Patients were divided into two groups of 50 no.’s each Group F- 3 ml 0.5% Heavy Bupivacaine & Fentanyl citrate 25 mcg, Group M –3 ml 0.5% Heavy Bupivacaine & MgSO4 100 mg were deposited intrathecally. Intraoperatively Sensory and Motor block onset and duration, HR, SBP, DBP & MAP, SpO2, side effects were assessed. Results: In group M– onset of sensory and motor block is significantly prolonged , duration of analgesia, motor block is comparable to group F and patients in group M were hemodynamically stable perioperatively, and at end of 24 hrs postoperatively VAS score was ≥ 3 at indicates a quality post operative analgesia. Conclusion: Fentanyl citrate as adjuvant to 0.5% heavy bupivacaine effectively augmented quality of spinal anaesthesia; its advantages are limited by incidence of side effects. MgSO4 100 mg provides excellent perioperative analgesia and stable hemodynamics and is an attractive non-opioid adjuvant alternative to fentanyl.