Our aim is to compare early versus late pancreatic stent placement in preventing PEP among patients with naive papilla. The EVL trial will provide essential answers regarding the optimal timing of prophylactic pancreatic stent placement in PEP prevention.All patients with difficult biliary cannulation undergoing endoscopic retrograde cholangiopancreatography (ERCP) with pancreatic guidewire-assisted technique for biliary access will be told about the opportunity to participate in EVL research. In total, 768 patients will be randomly assigned (1:1) to two arms: (1) early pancreatic stent placement (EPSP) (a pancreatic stent will be placed immediately after endoscopic retrograde cholangiography (ERC) or endoscopic sphincterotomy (EST)) and (2) late pancreatic stent placement (LPSP) (a pancreatic stent will be placed after all completion of therapeutic biliary procedures, e.g. biliary stone removal or drainage).The primary outcome is the rate and severity of PEP. The secondary outcomes are hyperamylasemia, the rate of stenting success, and other ERCP-related adverse events (AEs).