Fine wires (with a diameter less than 0.4 mm) have been extensively used for precision machines and other devices. It is well known that finely drawn wires have a much higher tensile strength than thick drawn wires. In the drawing process, a large shear deformation zone with a hardened layer, known as the “additional shear strain layer”, is generated beneath the surface layer of the wire. It was clarified that the depth of this additional shear strain layer was about 0.04 mm for wires of various diameters. As the diameter becomes small, the area ratio of the additional shear layer increases. Hence, the additional shear strain layer is a factor contributing to the high tensile strength of fine wires. In this paper, the main purpose is to discuss the cause of the increase in the tensile strength of the additional shear strain layer metallurgically. Thus, the crystal orientation and microstructure was measured by the Electron Back-Scatter Diffraction (EBSD) method. It was ascertained that the crystal of the surface layer was subdivided more finely than the center, and then the tensile strength of the surface layer increased.