Background: numerous researches have proved the benefits of laparoscopic cholecystectomy compared to the open method, mainly because of less metabolic response to stress, maintenance of diaphragm and pulmonary function, less postoperative complications, lower incidence of postoperative ileus, early mobilization, shorter hospital stay, and a more cosmetic. The main presentation of postoperative pain is somatic, whereas visceral pain is less present, and thus the pain is less in the patients operated by laparoscopic method. Aim of the Work: to compare intravenous Magnesium Sulphate with intra peritoneal Magnesium Sulphate as adjuvant to general anesthesia for pain management in laparoscopic cholecystectomy. Patients and Methods: this prospective randomized double blind clinical study using closed envelopes method was carried out on 100 adult patients, Undergoing laparoscopic cholecyctectomy in Bab-Alshaeria University Hospital, faculty of medicine, Al-Azhar University. After approval by the Institutional Ethical Committee, and informed written consent obtained from the patients, we randomly divided the patients into two groups 50 patients each. Results: the pain scores of group II (intra-peritoneal group) were significantly lower than group I (intravenous group), the total opioid consumption postoperatively in group II(intra-peritoneal group) was highly significant lower than group I (intravenous group). Also there was a significant reduction in opioid-related side effects such as postoperative nausea and vomiting. Conclusion: the intraperitoneal administration of magnesium sulphate is a safe and effective method in the management of acute postoperative pain after laparoscopic cholecystectomy more than intravenous administration of magnesium sulphate.