Background: Laparoscopic cholecystectomy as opposed to open cholecystectomy is currently the most accepted surgical technique for cholelithiasis. Intraperitoneal administration of some drugs can be effective for pain relief after laparoscopic surgery. Intraperitoneal instillation of local anesthetics and opioids is gaining popularity for better pain relief. Objectives: To compare the effect of adding dexamethasone or magnesium sulphate to bupivacaine on quality and duration of analgesia after intra-peritoneal instillation after laparoscopic cholecystectomy. Patients and methods: Our prospective study was conducted on sixty patients with ASA physical status I or II. Their ages ranged between 18-60 years scheduled for laparoscopic cholecystectomy under general anesthesia in Menoufia University Hospitals. Patients were randomly divided into three groups, 20 patients each. Patients in group B (bupivacaine group): received 25 ml 0.25% bupivacaine. Group M (Magnesium sulphate group) received 20 ml 0.25% bupivacaine and 5 ml (500 mg) magnesium sulphate.Group D (Dexamethasone group) received 20 ml 0.25% bupivacaine and2 ml (8mg) dexamethasone completed to 25 ml with 3 ml normal saline. Results: First time of analgesia was significantly longer among magnesium group than dexamethasone group and bupivacaine group (p < 0.05). Nalbuphine consumption in 24 hrs, was higher among bupivacaine group followed by dexamethasone group then magnesium group (p < 0.05). Also, VAS score was significantly higher in bupivacaine group at 4 hour than other groups and, at 6-hour it was higher in dexamethasone group and bupivacaine group with no significant difference but highly significantly more than magnesium. In magnesium group VAS score was low over 24 hours. Conclusion: Our study found that magnesium sulphate is a good additive than dexamethasone when combined with bupivacaine in intra-peritoneal instillation as it prolonged the duration of analgesia and reduced postoperative pain scores and nalbuphine consumption after laparoscopic cholecystectomy.