Objective To analyze the reliability of the Boston bowel preparation scale (BBPS) for the assessment of bowel preparation quality. Methods Demonstration video of Boston bowel preparation scale provided by Boston Medical Center were viewed by 49 clinicians,who came from several hospitals in Guangdong province and participated in an education conference.Then 3 testing colonoscopy videos were scored with BBPS and inter-observer reliability was assessed. 13 participants repeated the above test 3 months later,and intra-observer reliability was assessed.Results The correlation coefficient of inter-observer for BBPS scores was 0.987 (95％ CI:0.949 - 1.000 ),and that of intra-observer was 0.713(95 ％ CI:0.452 -0.849).Conclusion BBPS is a reliable measure of bowel preparation,while the validity of BBPS deserves further analysis.