Bowel preparation includes diet restriction and proper use of laxative before the colonoscopy, and this is one of the important factors to ensure a high quality colonoscopy. Suboptimal bowel preparation may lead to decreased ADR, cecal intubation rate, and surveillance interval and increased procedural time. Efforts to improve bowel cleansing quality through traditional communication routines, including face-to-face verbal education, written booklet or visual aids or telephone-based re-instruction have proven to be useful. A recent study using WeChat, a widely used social media mobile app in China, has also shown to be effectively improving bowel preparation level of a mixed population who received diagnostic (77%), screening (15.8%) and surveillance (7.2%) colonoscopy. However, the impact of social media mobile app on the bowel preparation level of screening colonoscopy is not yet known. Hence, this study will investigate the effectiveness of the most popular social media app worldwide, WhatsApp in bowel preparation level of screening colonoscopy.