A clinical efficacy study of 0.025-inch guidewires (GWs) according to mechanical property analysis has not been reported yet. This study was designed to evaluate the clinical efficacy of a newly developed 0.025-inch GW for biliary access according to the basic mechanical property. Commercially available 0.025-inch GWs were in vitro tested based on parameters of mechanical property. Patients with naïve papilla requiring diagnostic or therapeutic ERCP were randomly assigned to an experimental 0.025-inch newly developed GW or a control 0.025-inch GW group. Technical success rate of wire-guided cannulation (WGC), difficult biliary cannulation (DBC), and adverse event rates were measured in this multicenter randomized trial. The technical success rate of primary WGC was 79.1% (151 of 191) in the experimental group and 70.8% (131 of 185) in the control group (95% two-sided confidence interval: 8.25%;p< 0.001; for a noninferiority margin of 15%). The technical success rate including cross-over to each other was also non-inferior. However, the chi-square test showed a statistical difference (81.7%vs.68.1%;p= 0.002). Median biliary cannulation time was shorter in the experimental group (53 svs.77 s;p= 0.047). The rate of DBC was more frequent in the control group (34.6%vs.50.3%p= 0.002). Multivariate analysis revealed that control group was one of contributing factors for DBC. Overall rate of post-ERCP pancreatitis was not different (4.7%vs.8.6%;p= 0.125). WGC using a newly developed GW with superior physical performance GW in a bench test showed similar clinical efficacy and the rate of DBC was significantly lower in experimental GW.