BACKGROUND/AIMS: This study aimed to evaluate the feasibility and outcomes of mini-probe endoscopic ultrasound (mEUS) followed by submucosal saline injection (SSI-mEUS) for assessing the endoscopic resectability of colorectal subepithelial lesions (SELs). METHODS: From January 2020 to December 2023, the medical records of 391 SELs (364 patients) were retrospectively reviewed and categorized into no EUS, mEUS-only, and SSI-mEUS groups according to the procedure used. To compare variables between the SSI-mEUS and other groups, the no EUS and mEUS-only groups were combined into the non-SSI-mEUS group. In the SSI-mEUS group, submucosal cushion thickness was endosonographically measured after the saline injection. Treatment outcomes and histological diagnosis were retrospectively reviewed. RESULTS: A total of 210 lesions in the no EUS group, 23 in the mEUS-only group, and 125 in the SSI-mEUS group were endoscopically resected. The mean SEL size was larger in the SSI-mEUS than in the non-SSI-mEUS group (6.8 +/- 2.6 mm vs. 4.9 +/- 2.6 mm, p < 0.001). R0 resection was achieved in 107 of 110 neoplastic lesions (97.3%) in the SSI-mEUS group vs. 159 of 176 neoplastic lesions (90.3%) in the non-SSI-mEUS group (p = 0.046). Not using SSI-mEUS was the only factor associated with indeterminate or positive deep resection margins (odds ratio 3.45, 95% confidence interval 1.19-13.40, p = 0.021). CONCLUSION: For colorectal SELs, including those that appear insufficiently elevated during conventional endoscopy, SSI-mEUS enables an objective assessment of the feasibility of endoscopic resection and can predict a high likelihood of achieving a safe and complete resection.