Background/Aims: Application of polyglycolic acid (PGA) sheets using fibrin glue in post-endoscopic submucosal dissection (ESD) ulcers to prevent bleeding has been reported to be difficult with the conventional delivery method because of gravity. This study assessed the usefulness of the envelope-based delivery system with and against gravity in living pigs. Methods: PGA sheets were applied on post-ESD ulcers with and against gravity six times each using the conventional and envelope methods, respectively. The PGA sheet delivery time and the endoscopic and histological findings of the treated ulcer floors were compared. Results: With gravity, the median PGA sheet application time was 1.00 (0.68–1.30) min/cm2 and 0.32 (0.18–0.52) min/cm2 with the conventional and envelope techniques (p=0.002), respectively, and against gravity, it was 1.20 (1.13–1.63) min/cm2 and 0.50 (0.39–0.58) min/cm2 (p=0.002), respectively. Against gravity, the endoscopic and histological findings revealed that the conventional group had insufficient fixation of the PGA sheets, but the envelope groups had sufficient fixation. The results with gravity were similar between the groups. Conclusions The envelope method makes it possible to deliver PGA sheets to the stomach quickly and cover ulcers appropriately both with and against gravity in living pigs.