An experimental study is presented, of the effect of cemented carbide grade on the cutting performance in drilling 0.55% carbon steel by solid-boring-tools (BAT System) with 20mm diameter. The results are summarized as follows: (1) Cutting torque and thrust with (ISO) K type carbide tools are lower than with P type ones. It is due to the difference of built-up-edge formation on cutting edge. (2) Smoother surface and more accurate holes are produced with P type carbide tools than with K type carbide tools. (3) In cutting conditions with smaller size boring tools, longer tool life is obtained with K type carbide tools than with P type carbide tools, which are commonly used in large size deep-drilling.