In this study the effect of wiper cutting tool geometry and cutting tool nose radius was investigated on machining of ductile cast iron (DCI). In this purpose, turning test were carried out at three cutting speeds (200, 275 and 350 m/min), three feed rates (0.05, 0.15 and 0.15 mm/rev) and at a constant depth of cut (1 mm). In turning test were carried out dry cutting and coated cemented carbide was used as cutting tool. The results show minimum surface roughness were obtained 1.2 mm cutting tool nose radius. The best surface roughness was obtained in experiments at the big tool nose radius, high cutting speed and lower feed rate. According to the results the increasing cutting tool nose radius has a positive effect on the surface roughness.