If the diameter of the intrahepatic bile duct is much less dilated, bile duct puncture with a 19-gauge needle can be challenging during EUS-guided biliary drainage (EUS-BD). These characteristics can decrease the difficulty of bile duct puncture, but use of a 22-gauge needle is less feasible because of poor visibility, maneuverability, and stiffness of the conventional .018-inch guidewire. A novel, improved .018-inch guidewire has recently become available. We conducted a prospective study to evaluate the technical feasibility and safety of EUS-BD in patients with insufficient bile duct dilatation using a 22-gauge needle and the new .018-inch guidewire. A 22-gauge needle was used as the puncture needle for intrahepatic bile ducts of diameters<1.5mm, and a 19-gauge needle was selected for diameters≥1.5mm. As the primary endpoint of the study, the technical success rate of EUS-BD using a 22-gauge needle with the novel .018-inch guidewire was evaluated in patients with insufficient dilation of the intrahepatic bile duct. Forty-one patients who required EUS-BD were enrolled (22-gauge needle group, n= 18; 19-gauge needle group, n= 23). Technical success was obtained in all patients in the 19-gauge needle group. In the 22-gauge needle group, technical failure occurred in 2 patients because of nonidentification of the intrahepatic bile duct on EUS (technical success rate, 88.9%), and puncture of the bile duct itself was not performed in these patients. Mean procedure time was similar between the groups. Adverse events were observed in 16.7% of patients (3/16) in the 22-gauge needle group and in 34.8% of patients (8/23) in the 19-gauge needle group. Outcomes of using a 22-gauge needle with a novel .018-inch guidewire were comparable with a 19-gauge needle with a .025-inch guidewire, even in the case of insufficient intrahepatic bile duct dilatation. These results require verification in a prospective, randomized trial comparing 22-gauge and 19-gauge needles with a larger sample size. (Clinical trial registration number: UMIN000044441.).