Abstract. Drilling process has many applications including making molds and dies, all requires different quality of the drilled hole. The aim of this study is to establish models and optimization of cutting parameter to get the best hole quality, including enlargement diameter, circularity error and surface roughness in drilling hardened steel. Drilling experiments have been performed using different cutting parameters (i.e. cutting speed and feed rate) and employ and uncoated carbide drill under flooded cooling. The experimental results show that both of the cutting speed and feed rate significantly affect all responses. Models for responses have been developed for investigation in this study, and their optimizations have been obtained, showing better quality of the drilled hole produced at higher cutting speed and lower feed rate. Desirability for the optimum criteria is 0.944 at the highest cutting speed (60 m/min) and lowest feed rate (0.05 mm/rev).