Background: For flat and/or depressed lesions ranging from 11-20 mm, hybrid ESD, i.e., EMR with circumferential incision (CI), is now prevalent. However, there is no clear standard for choosing an injection solution. Sodium hyaluronate (SH) is often used, despite its disadvantages. This study aimed to clarify the most effective injection solution for safe hybrid ESD for trainees in various gastrointestinal tract organs. Methods: CI was performed on 30 resected porcine esophagi, stomachs, duodena and colons. The following three solutions were injected into submucosa, and their ability to maintain mucosal elevation height (MEH) was evaluated: Solution A, normal saline (NS); Solution B, 1:1 mixture of NS and 0.4% SH; and Solution C, 0.4% SH. We measured the minimum snarable MEH and the average procedure time for snaring, and the optimal concentration of SH was identified both graphically and histopathologically. Results: The lesion-lift ability was superior at higher SH concentrations except, for duodenum. No solution obtained sufficient MEH in duodenum. The minimum snarable MEH was 5.02 mm, 5.73 mm, and 6.05 mm, and the snaring procedure time was 58.8 s, 56.2 s, and 75.3 s in esophagus, stomach, and colon, respectively. Hybrid ESD could be performed successfully with Solution B for esophagus, Solution A for stomach and Solution C for colon, and these results were confirmed histopathologically. Conclusions: The optimal solutions for hybrid ESD in an ex-vivo porcine model for trainees were Solution B for esophagus, Solution A for stomach, and Solution C for colon. Further study is needed for duodenum.