Postoperative nausea and vomiting is (PONV) a very distressing complication and preventive measures are justified when the risk of PONV is very high. Ondansetron is the first 5-HT3 antagonist used alone or in combination for prophylaxis of PONV due to its lower cost. Granisetron is recently introduced 5-HT3 antagonists with greater affinity for 5-HT3 receptor and having longer half-life. Aim of the present study is to compare the antiemetic efficacy of ondansetron, granisetron in high-risk patients undergoing laparoscopic cholecystectomy under general anaesthesia. Method: Thisstudy was prospective and randomized one. Written informed consent will be taken from patients in both groups. Patients will be kept NPO for 12 hours before surgery. In the preoperative room, iv line will secured. In the operation theatre ASA Standard monitoringdevices pulse oximetry, NIBP, ECG will be attached and baseline blood pressure, heart rate and O2 saturation values will be recorded. Later capnograpy will be attached after theintubation