Bowel cleansing efficacy was assessed using Boston bowel preparation scale. Vital signs and laboratory tests were checked before colonoscopy. Study participants completed questionnaire which contained patient's satisfaction, tolerability, and adverse event during bowel cleansing. Bowel cleansing efficacy, patient's tolerability, and safety profile were compared between the two groups. Successful bowel cleansing was estimated 85% for split dose group. We set 10% for inferior margin. Considering 10% drop out, a total of 352 subjects will be recruited.