Inadequate bowel preparation for colonoscopy can lead to increased procedural time, decreased diagnostic yield and an increase in complication rate. Fear, anxiety and lack of information reported by patients are barriers for optimal colonoscopy screening procedures. The successful outcome of colonoscopy procedure depends on how well the colon is prepared enhancing accurate visualisation. This study intended to determine the effectiveness of video instruction regarding bowel preparation on anxiety, knowledge of procedure and quality of bowel cleanliness among patients undergoing colonoscopy. Using quantitative approach, an experimental study was undertaken for 6 weeks. One hundred and twenty patients undergoing colonoscopy were selected using consecutive sampling techniques and were randomly allocated to the control and experimental group. State trait anxiety inventory, knowledge questionnaire and the Boston bowel preparation scale were used to collect the data. The experimental group received the video-assisted teaching on bowel preparation and the control group received the standard teaching. The quality of bowel cleanliness was found to be excellent in 25% of patients in the control group and 75% of patients in the experimental group. There was a significant decrease in the mean score of anxiety level from 45.05 to 34.40 in the experimental group. The study revealed that there was a significant relationship between knowledge of procedure and quality of bowel cleanliness in the experimental group (r = 0.35, P