Abstract Backgrounds and study aims Gel immersion endoscopy is a novel technique to secure the visual field during endoscopy. The aim of this study was to develop a dedicated gel for this technique. Methods To identify appropriate viscoelasticity and electrical conductivity, various gels were examined. Based on these results, the dedicated gel “OPF-203” was developed. Efficacy and safety of OPF-203 were evaluated in a porcine model. Results In vitro experiments showed that a viscosity of 230 to 1900 mPa·s, loss tangent (tanδ) ≤ 0.6, and hardness of 240 to 540 N/cm2 were suitable. Ex vivo experiments showed electrical conductivity ≤ 220 μS/cm is appropriate. In vivo experiments using gastrointestinal bleeding showed that OPF-203 provided clear visualization compared to water. After electrocoagulation of gastric mucosa in OPF-203, severe coagulative necrosis was not observed in the muscularis but limited to the mucosa. Conclusions OPF-203 is useful for gel immersion endoscopy.