© 2015 Korean Society of Gastrointestinal Endoscopy. Background/Aims: Intestinal lavage (IL) administration immediately before capsule enteroscopy (CE) is superior to lavage the day before the procedure. We aimed to determine the effect of IL timing on CE diagnostic yield. Methods: Patients referred for CE were randomized prospectively into two equal groups according to the timing of IL with 2 L of polyethylene glycol solution. Group A and B underwent IL over 2 hours beginning 14 and 4 hours, respectively, before the scheduled CE. The primary outcome measure was preparation quality, measured with a predetermined validated grading scale. Results: A total of 34 patients were randomized. The frequency of mucosal abnormalities (77% vs. 82%, p=not significant [NS]) and diagnostic yield (47% vs. 53%, p=NS) were similar between the two groups. Moreover, no significant association between the quality of small bowel preparation and the timing at which the purgative for IL was administered was observed (overall fluid transparency, p=0.936; overall mucosal invisibility, p=0.091). Conclusions: Day-before IL is equivalent to same-day IL in terms of overall preparation quality, proportion of complete studies to cecum, small bowel transit time, frequency of identified mucosal abnormalities, and overall diagnostic yield.