Background/Aims: Polyethylene glycol (PEG)-based gut la￢vage solutions are safe and effective, but require the intake of large volumes of fluid. The use of 2 L PEG plus 45 mL sodium phosphate (PEG2 plus NaP) was compared with 4 L PEG (PEG4) for bowel cleansing before colonoscopy. Meth￢ods: Patients were randomized to the PEG2 plus NaP group or PEG4 group between January 1, 2009 and March 31, 2010. One hundred and thirty patients were included in the PEG2 plus NaP group, and 141 patients in the PEG4 group. Results: The qualities of the bowel preparation, based on the Ottawa scale were not significantly different between the groups (4.8±2.25 for the PEG2 plus NaP group vs. 5.11±2.26 for the PEG4). In addition, there were no significant differenc￢es in side effects. Laboratory findings after bowel prepara￢tion, including electrolyte, phosphorus and creatinine levels, were within the normal ranges in both groups. Conclusions: PEG2 plus NaP provides good cleansing that is similar to PEG4, but with a lower volume. However, because PEG2 plus NaP can cause serious side effects such as calcium deposi￢tion in the kidneys (i.e., nephrocalcinosis), this solution might be considered for the outpatients who cannot tolerate PEG4.