Background : Spinal anaesthesia is the most common procedure done for caesarean sections. The aim was to evaluate the duration of sensory blockade on addition of magnesium sulphate to intrathecal hyperbaric bupivacaine for prolongation of the same. Methods : 100 parturients undergoing caesarean section were divided into two groups of 50 each. Group N received 10mg of bupivacaine with 0.1cc NS and Group M 10mg bupivacaine with 50 mg magnesium sulphate. The Statistical software Open Epi, Version 2.3 was used for the analysis of the data. Results : The average duration of spinal analgesia in Group N was 104.45 + 18.38mins whereas it was 205.45 + 6.36 mins in Group M with a significant p value of < 0.001. Conclusion : Addition of magnesium sulphate significantly prolongs the duration of sensory blockade in parturients undergoing elective caesarean sections, henceforth decreasing the need for a rescue analgesic.