Introduction: Endoscopic submucosal dissection (ESD) is a well-established treatment for gastric cancer limited to the mucosa. ESD allows en bloc resection of lesions >10mm with increased complete resection rate and low recurrence rate compared to endoscopic mucosal resection. Few studies have compared the efficacy and safety of ESD knives. We present a prospective, randomized study comparing three mechanistically different ESD knives in the porcine model. Methods: In this prospective, randomized study, three different ESD knives were compared: Dual (KD-650L, Olympus), IT2 (KD-611L, Olympus) and Hybrid T-type (20150-060, ERBE). Twelve Yorkshire pigs weighing 33-50 kg underwent two esophageal and four gastric mucosal resections. A computergenerated randomization sheet was used to assign the type of knife for each resection site. The primary end point was total operative time (OT). Secondary outcomes were effects of lesion location and learning curve on OT, significant hemorrhage requiring the use of coag-grasper, macroscopic perforation, and injuries and depth of injuries as assessed histologically by a pathologist blind to the type of knife used. Results: HKT (average OT 27 minutes) was faster than Dual knife (average OT 27 minutes, 36 minutes, p < 0.05). HKT was faster than IT2 knife, but the difference was statistically insignificant. There were no statistically significant differences in hemorrhage, thermal injury to mucosa, injuries to muscularis propria, and mean size of resection specimen among the knives. No macroscopic perforations were present.Mean OT for gastric ESD was shorter than that for esophageal ESD (24 min, 41 min, p= < 0.01) and mean OT for proximal gastric lesions was shorter than that for distal ones(20 vs 29 min, p < 0.02). Conclusion: All three knives displayed equal efficacy in tissue removal as they all achieved complete resection of target mucosa. It appears that HKT is marginally faster than Dual and IT2 knives, which may be partially due to its ability to perform injections without change of accessories. Our study indicates that location of the lesion had a more significant effect on the OT than the type of knife used. For proximal gastric resection, the OT decreased significantly after the first seven ESDs. This was found to be true for all three knives. Our results confirm prior studies indicating that while there is a learning curve, the slope of the curve is not steep, possibly due to the operator's significant experience with the procedure.Table: Table. Mean Operating TimeFigure: Resection crater being assessed for perforations and bleeding.Figure: Learning effect demonstrated by decrease in operating time after first 7 ESDs.