In this study, effects of different machining parameters on surface roughness in turning of St-37 material are presented. The machining experiments were carried out on the CNC lathe. In order to minimize the number of experiments, the experimental design was set up using Taguchi's L27 orthogonal array. Cutting speed (150 m/min, 200 m/min, and 250 m/min), feed rate (0,1 mm/rev, 0,2 mm/rev, and 0,3 mm/rev), depth of cut (0,5 mm, 1 mm, and 1,5 mm), and tool nose radius (0,4 mm, 0,8 mm and 1,2 mm) were used as control factors. The analysis of variance (ANOVA) was performed in order to determine the impact of the control factors on surface roughness. Signal/noise (S/N) ratios were determined in the Taguchi design. The results of the regression models and Taguchi Analysis revealed that the most effective parameters on surface roughness (Ra and Rz) were the feed rate (f) and tool nose radius (R).