AISI 4140 steel material has a wide range of usage in the industry. Before this material is hardened, rough turning is performed. Besides the surface roughness value is very important in terms of machinability. In this experimental study, the effect of cutting parameters on surface roughness (Ra and Rz) during the turning of AISI 4140 steel was analyzed using the Taguchi method. This study, Taguchi L9 was designed in 3 different cutting speeds (100, 140 and 180 m min-1), 3 different feed rates (0.08, 0.12 and 0.16 mm rev-1), and 3 different depth of cut (0.5, 0.9 and 1.3 mm). In the analysis of experimental data, S/N (signal/noise) ratios and variance analysis were used to analyze the effect of cutting parameters on the surface roughness value. The degrees of influence on Ra according to S/N ratios are the feed rate ( f ), cutting speed (V), and depth of cut (a), respectively, from large to small. On Rz, the effects of cutting parameters respectively were observed to be in f, a, and V. The f on surface roughness values (Ra and Rz) was found to have an effect of 99.34% and 98.47%, respectively.