High-speed machining thoroughly hardened tool steels has emerged as a competitive finishing technology for making dies and molds. The objective of this paper is to develop an optimization method for the better (i. e., lower value) surface roughness in terms of cutting parameters when high-speed milling hardened H13 steel. The cutting parameters to be considered were cutting speed, feed per tooth, radial depth of cut, and axial depth of cut, respectively. A series of high-speed milling experiments of hardened H13 steel using PVD coated carbide inserts without any cutting fluids were performed to measure the surface roughness data. Taguchi orthogonal arrays, signal-to-noise (S/N) ratio, and analysis of variance (ANOVA) were used to evaluate the effects of cutting parameters on surface roughness and to find the optimal factor/level combination for the better surface roughness. The investigations of this study would be used for design optimization of cutting parameters to obtain the better surface roughness.