This methodology investigates the determination of the fracture toughness of 3D-printed specimen, under monotonic loading conditions. The application is based on the use of a Single Edge Notch Bending (SENB) specimen made by a 3D-printing process (stainless-steel 17-4PH). The load-displacement curves exhibited linear behavior until crack initiation, indicating that the Linear Elastic Fracture Mechanics (LEFM) can be used under the small-scale yielding assumption. The methodology established in the paper represents the major outcome to characterize the fracture toughness of the material. The aim of the paper is twofold. The one is to describe the procedure allowing the identification of the crack initiation through the monitoring of the Crack Mouth Opening Displacement (CMOD), and the second is to determine the critical fracture toughness of the 3D-printed material of the specimen.