Background <p>Gel immersion endoscopy is a novel method that uses gel to enhance the visual field. This study aimed to analyze the efficacy of magnified endoscopy under gel immersion for optimal visualization and characterization of colorectal tumors.</p> Methods <p>We retrospectively examined 107 lesions observed with blue-laser/light imaging (BLI) or narrow-band imaging (NBI) between June 2022 and July 2023 using the Japan NBI Expert Team classification. The lesions underwent magnified endoscopy first with CO₂ insufflation, then underwater, and finally under gel immersion. Visualization quality and diagnostic accuracy were evaluated. All colonoscopies were performed by three endoscopists (experienced: 2, less experienced: 1).</p> Results <p>Among the 107 lesions, the mean tumor size was 22.7 ± 11.8&#xa0;mm and 58 lesions were non-polypoid. Histopathology revealed 15 sessile serrated lesions, one sessile serrated lesion with dysplasia, 36 low-grade dysplasias, 37 high-grade dysplasias, 14 adenocarcinoma (≥ T1) cancers, and four others. Gel immersion resulted in significantly less halation compared to CO₂ insufflation (<i>p</i> &lt; 0.0001), fewer bubbles than underwater (<i>p</i> &lt; 0.0001), and less intestinal fluid compared to both CO₂ insufflation and underwater (<i>p</i> &lt; 0.0001). Visualization quality was significantly better with gel immersion than with CO₂ insufflation and underwater (<i>p</i> &lt; 0.0001). No significant differences were observed in the accuracy of the tumor characterization among the three methods.</p> Conclusions <p>The reduced halation, bubbles, and internal fluid with gel immersion provided excellent visualization. The diagnostic accuracy for colorectal lesions using the gel immersion method was comparable to that of CO₂ insufflation and underwater methods.</p>