Background: Capsule endoscopy is a novel non-invasive method for visualization of the entire small bowel. The diagnostic yield of capsule endoscopy depends on the quality of visualization of the small bowel mucosa and its complete passage through the small bowel. To date, there is no standardized protocol for bowel preparation before capsule endoscopy. The addition of simethicone in the bowel preparation for the purpose of reducing air bubbles in the intestinal lumen had only been studied by a few investigators. Methods: Sixty-four participants were randomly divided into two groups to receive a bowel preparation of polyethylene glycol (PEG) solution (Group 1) and both PEG solution and simethicone (Group 2). The PEG solution and sime- thicone were taken the night before and 20 min prior to capsule endoscopy, respectively. Frames taken in the small intestine were examined and scored for luminal bubbles by two professional capsule endoscopists. Gastric emptying time and small bowel transit time were also recorded. Results: Simethicone significantly reduced luminal bubbles both in the proximal and distal small intes- tines. The mean time proportions with slight bubbles in the proximal and distal intestines in Group 2 were 97.1% and 99.0%, respectively, compared with 67.2% (P<0.001) and 68.8% (P<0.001) in Group 1. Simethicone had no effect on mean gastric emptying time, 32.08 min in Group 2 compared with 30.88 min in Group 1 (P=0.868), but it did increase mean small intestinal transit time from 227.28 to 281.84 min (P=0.003). Conclusion: Bowel preparation with both PEG and simethicone significantly reduced bubbles in the intestinal lumen and improved the visualization of the small bowel by capsule endoscopy without any side effects observed. Background: Capsule endoscopy is a novel non-invasive method for visualization of the entire small bowel. The diagnostic yield of capsule endoscopy depends on the quality of visualization of the small bowel mucosa and its complete passage through the small bowel. To date, there is no standardized protocol for bowel preparation before capsule endoscopy. The addition of simethicone in the bowel preparation for the purpose of reducing air bubbles in the intestinal lumen had only been studied by a few investigators. Methods: Sixty-four participants were randomly divided into two groups to receive a bowel preparation of polyethylene glycol (PEG) solution (Group 1) and both PEG solution and simethicone (Group 2). The PEG solution and sime- thicone were taken the night before and 20 min prior to capsule endoscopy, respectively. Frames taken in the small intestine were examined and scored for luminal bubbles by two professional capsule endoscopists. Gastric emptying time and small bowel transi The mean time proportions with slight bubbles in the proximal and distal intestines in Group 2 were 97.1% and 99.0%, respectively, compared to those in proximal and distal intestine in Group 2 with 67.2% (P <0.001) and 68.8% (P <0.001) in Group 1. Simethicone had no effect on the mean gastric emptying time, 32.08 min in Group 2 compared with 30.88 min in Group 1 did increase mean small intestinal transit time from 227.28 to 281.84 min (P = 0.003). Conclusion: Bowel preparation with both PEG and simethicone significantly reduced bubbles in the intestinal lumen and improved the visualization of the small bowel by capsule endoscopy without any side effects observed .