Two hundred and eighteen patients were assinged to one of three groups in a prospective, double blind, randomized manner. Group U, the control group, received undiluted propofol (10 mg/ml); Group D1, diluted propofol (5 mg/ml); Group D2, diluted propofol (2.5 mg/ml). All patients were topicalized with 2% viscous lidocaine and 10% lidocaine spray for topical anesthesia and pethidine 0.5 mg/kg, midazolam 0.05 mg/kg and propofol 1 mg/kg for premedication and induction Anesthesia was maintained with continuously intravenous infusion of titratable propofol. Blood pressure, heart rate, ECG, oxygen saturation at base line, after premedication, immediately and every 5 minutes after induction, total dose of propofol, duration of anesthesia and complications were recorded. The results of the study showed that total doses and dose requirement of propofol and complications in Group U were higher than that of Group D1 and D2 with a statistically significant level of p < 0.001. It can be concluded that diluted propofol is safe and effective for the patients who have been undergoing ERCP.