Aim : The study was undertaken to compare the efficacy of Magnesium sulphate with  potassium chloride as an adjuvant for post operative analgesia in USG guided SCB. Materials and methodology: The patients were randomly divided into 3 groups of 20 each into group A (KCl – 0.2 mmoles(1ml solution)), group B (MgSO₄ –150mg (1ml solution)) and group C (Control–1 ml NS) added as adjuvant in USG guided SCB .  Duration of effective analgesia  and side effects ,if any were noted. Observation: The duration of effective analgesia was found to be 261.25 ± 46.84 minutes in Group B: Magnesium sulphate (150mg) followed by 216.15 ± 63.06 minutes  in Group A: Potassium chloride (0.2mmoles) and lastly 180.25 ± 16.42 minutes in  Group C: Control. Conclusion: Magnesium sulphate (150 mg )as an adjuvant in USG guided SCB  is better than potassium chloride (0.2mmoles) for post operative analgesia in adult surgical patients