In this randomized controlled study, consecutive outpatients scheduled for elective colonoscopy were randomized into two groups. Group A patients (n = 150) used 2 L PEG before colonoscopy. Patients in group B (n = 150) were additionally advised to chew sugarless gum plus 2 L PEG, The overall quality of colonoscopy cleaning was evaluated using the Boston Bowel Preparation Scale by endoscopists who was blinded to the intervention. Difficulty of procedure, patients' tolerance, and adverse events were also evaluated.