Suturing of a mucosal defect after gastric endoscopic submucosal dissection (ESD) reduces the incidence of adverse events and shortens hospitalization. However, post-ESD mucosal defects are circular, large, and with a thick mucosal layer, which are difficult to suture using conventional clips alone. The MANTIS Clip (Boston Scientific Japan, Tokyo, Japan) is a reopenable, rotatable through-the-scope clip designed for large defect closure. It uses anchor prongs to securely grasp wound edges. The initial use of the MANTIS Clip significantly reduces mucosal defects, which then allows for easy suturing with conventional clips. We herein report a case in which the MANTIS Clip was useful for suturing a mucosal defect after gastric ESD.