Tool steels have important participation in the worldwide market of steels. They are used by metal-mechanical industry as cutting tools, molds, punches, etc. Because the use is of great responsibility, it is important to discuss the relationship between microstructure and mechanical properties. The starting material was powder of a commercial tool steel with the composition (wt%) 2.5%C, 5.25%Cr, 0.9%Si, 9.75%V, 0.5Mn, 1.3%Mo and balance Fe. The samples were obtained by hot isostatic pressing (hip) process, and than were austenitizing at 1120°C and submitted to tempering in the temperature range varying from 430° to 550°C. The aim of this work was to evaluate the correlation between heat treatment, microstructure and mechanical properties. Results of toughness and hardness are presented.