The present study was a prospective, randomized study, undertaken to evaluate the antiemetic efficacy of ondansetron and granisetron when used alone in the prevention of postoperative nausea and vomiting in patients undergoing laparoscopic cholecystectomy.Granisetron (0.04 mg/Kg ) given prophylactically one minute before the start of anaesthesia results in statistically significant reduction in the incidence of nausea and vomiting when compared with Ondansetron (0.1mg/Kg ); Granisetron having a prolonged duration of action. The difference between the two groups becoming more evident during the latter part of the study period.Granisetron is superior to Ondansetron in providing prolonged efficacy in preventing post operative nausea and vomiting.