Vigorous intravenous fluid resuscitation (IVFR) was reported to reduce post-endoscopic retrograde cholangiopancreatography (ERCP) pancreatitis in a pilot study. We performed a randomized, double-blind controlled trial to establish whether periprocedural vigorous IVFR reduces the risk of post-ERCP pancreatitis. A total of 510 patients with native papilla at 3 tertiary referral centers in Korea were randomly assigned (1:1) to groups given vigorous IVFR (lactated Ringer's solution in an initial bolus of 10 mL/kg before the procedure, 3 mL/kg/h during the procedure, for 8 hours after the procedure, and a post-procedure bolus of 10 mL/kg) or a standard IVFR (lactated Ringer's solution at 1.5 mL/kg/h during and for 8 hours after the procedure). The primary end point of the study was the development of post-ERCP pancreatitis, and the secondary end point was severity of pancreatitis, hyperamylasemia, and fluid overload. The main indications for ERCP were choledocholithiasis (58%) and malignant biliary stricture (27%). Post-ERCP pancreatitis developed in 11 patients in the vigorous IVFR group (4.3%) and 25 patients in the standard IVFR group (9.8%) (relative risk, 0.41; 95% CI, 0.20-0.86; P= .016). Moderate or severe acute pancreatitis occurred in a significantly smaller proportion of patients in the vigorous IVFR group (0.4%) than in the standard IVFR group (2.0%; P= .040). One patient in the vigorous IVFR group developed peripheral edema. In a double-blind, randomized controlled trial, we found vigorous periprocedural intravenous hydration with lactated Ringer's solution to reduce the incidence and severity of post-ERCP pancreatitis in average-risk and high-risk cases. IVFR is not associated with increased adverse events. ClinicalTrials.gov number: NCT02308891.