Cold work tool steels are high alloy tool steels, which are generally used up to an operating temperature of 250°C. They are mainly used as materials for pressing, stamping and fine blanking tools. The desired properties of tool steels are achieved due to complex alloy systems. The motivation of this work is to elucidate the influence of Cobalt on compressive strength. Powder metallurgical produced cold work tool steel with various cobalt contents served as test material. The mechanical properties have been investigated by compression tests and impact bending tests and microstructures was characterized using SEM analysis. The experiments showed that the influence of cobalt on tool steels reported in literature is also valid for the high Vanadium cold work tool steel investigated in this work. For example, the increase of cobalt content leads to an increase of the secondary-hardening peak and a shift of the hardening peak to lower tempering temperatures. Investigations by scanning electron microscope revealed that the solubility of MC-carbides is enhanced with increasing cobalt content. Similar to an increase in the austenitization temperature Cobalt leads to a stronger solution of the carbides and, thus, to a higher fraction of dissolved carbide forming elements in the matrix. The higher content of carbide forming elements results in an increase in the secondary-hardening peak. There seems to be no major influence on the mechanical properties if the solution state has been set by the austenitization temperature or cobalt content.