Background: Perioperative analgesia has been administered traditionally as opioid analgesics, but routine use of opioids for postoperative analgesia has recently been critically challenged. Excessive use of potent opioids may actually increase postoperative pain as a result of rapid elimination and development of acute tolerance and decrease patient satisfaction. Objective: The aim of this study was to assess and compare the effect of IV infusion of lidocaine and magnesium sulphate (Mg) as adjuvant for postoperative pain in anal surgery after spinal anesthesia regarding duration, potency of analgesia, analgesic consumption and hemodynamics. Patients and methods: In this prospective, observational, randomized, double blinded (nurse and junior doctor) placebo study, 150 patients of ASA (American Society of Anesthesiologists) physical status I and II with the age between 18-40 year, undergoing anal surgery under spinal anesthesia were included. The study was conducted in Al-Azhar University Hospital, Assiut during the period from June 2018 to Oct 2018. Results: The results showed that there were significant differences between the three groups according to BP and HR. The patients in Mg group showed more hypotension and bradycardia than the patients in lidocaine and placebo groups. Patients in Mg group showed lower VAS score than lidocaine and placebo groups. The amount of analgesic consumption was lower in Mg group than lidocaine and placebo groups. Conclusion: Usage of IV MgSO4 at 50 mg/kg followed by continuous infusion of 10 mg/kg/h leading to decrease in postoperative pain and analgesic consumption in patients undergoing anal surgery under spinal anesthesia.