Background <p>Obesity and body mass index (BMI) have been reported as risk factors associated with inadequate bowel preparation, however, conflicting results have been consistently reported. This study aims to explore the association between obesity and the quality of bowel preparation.</p> Methods <p>We evaluated the efficacy of bowel preparation and colonoscopy outcomes according to obesity and BMI in subjects who underwent screening colonoscopy at a single hospital between January 1, 2021, and December 31, 2022. Overall, the quality of bowel cleansing was assessed using the Boston Bowel Preparation Scale (BBPS).</p> Results <p>The 4,699 subjects who underwent screening colonoscopy were classified as the non-obese (n = 3058, 65.1%) and obese (n = 1641, 34.9%) groups. The quality of bowel preparation measured by the efficacy of preparation in each segment, overall high-quality cleaning and successful cleansing, and rate of colonoscopy termination due to inadequate preparation were not significantly different between the non-obese and obese groups and according to BMI subgroups, before and after propensity score matching. Polyp and adenoma detection rates were significantly higher in the obese group than in the non-obese group after propensity score matching for age, sex, diabetes, history of abdominal surgery and type of preparation agent (60.1% <i>vs</i> 55.3%, <i>p</i> = 0.006 and 39.2% <i>vs</i> 36.0%, <i>p</i> = 0.058, respectively).</p> Conclusions <p>Obesity and BMI were not associated with suboptimal preparation for colonoscopy when low-volume agents were used. Obese group may be considered a higher-risk population for colonic neoplasia, and given adequate bowel preparation, they are well suited for screening colonoscopy.</p>