The application of Ni-hard 4 cast irons are similar to high chromium cast irons but the characteristic which differs Ni-hard 4 ‎cast iron from high  chromium cast irons is its great hardenability. In the present research the effect of tungsten on Ni-hard 4 cast ‎irons and its effect on the microstructure and formation of carbides are investigated. Also the aim of this research is to ‎simultaneously increase the impact resistance and toughness. For this reason samples according to ASTM A532 standard were ‎prepared without the addition of tungsten while the other samples were prepared by adding different percentages of tungsten to ‎the melt by casting method. After the casting procedure; heat treatment, impact, macro-hardness and micro-hardness tests were ‎done. Studies showed that the addition of tungsten leads to the increase in the hardness of the matrix phase and the formation of ‎M7C3 carbides and it also increases the volume fraction of the carbides and decreases the average diameter of carbides. Due to ‎these reasons the hardness and impact resistance simultaneously increase.‎