This research is to determine the influence of the process parameters when machining SKD11 steel and proposes the optimized technical conditions to minimum surface roughness (Ra) in WEDM (Wire Electrical Discharge Machining) process. Process parameters such as cutting voltage (VM), pulse on time (Ton), pulse off time (Toff), servor voltage (SV), wire feed (WF) and cutting speed (SPD) were investigated as input variables. To find out the optimized paramaters, Taguchi method was used to design experimental plans. With this method, 18 experimental runs were conducted with six above process parameters. The experimental results show that surface roughness (Ra) is minimum with optimized parameter set as follows: SPD = 4 m/min, Ton = 6 s; Toff = 16 s; SV = 34 V; WF = 10 mm/min and VM = 6 V. The deviation value between calculation and experiment is 9.29 %.