Cold-work tool steels contain high-carbon, high-chromium or group D steels, AISI D2is recommended for tools requiring very high wear resistance, combined with moderate toughness (shock – resistance), due to some of mechanical properties are not covered and needed to be improved by changing microstructure. This work was to study the effect of heat treatment on microstructure, hardness, impact and tensile test in D2 tool steel. Optical microscopy (Oly Maps Microscope) was used to examine the microstructural basis, the mechanical properties were observed from the investigation that both hardness and tensile test values were significantly increased with increasing of tempering temperature by using oil or air quenching media. At the same time the impact value was constant. The mechanical properties has been improved due to the D2 tool steel was austenitezed at 1050℃ for half hour time and tempered for different temperature and quenched.