Abstract: Objective To study the effect of oral simethicone on removal of air bubbles in colonoscopy. Methods Patients in oral simethicone group were given oral sodium phosphate followed by 500 ml water containing 30 ml simethicone while those in control group were given only 500 ml water. Their abdominal distension was assessed immediately after endoscopy. Results The number of air bubbles in colon and abdominal distention were compared between the two groups after colonoscopy. The effect of simethicone on removal of air bubbles was better in oral simethicone group than in control group(P< 0.05). Conclusion Oral imethicone can effectively remove air bubbles in colon before painless colonoscopy and prevent abdominal distention after colonoscopy.