Thermal stability and phase transformation temperatures in Firth-Vickers 535 (12Cr–Mo–VNbWCo) steel have been studied by differential scanning calorimetry and dilatometry. The (M s), (Ac 1) and (Ac 3) temperatures of this steel were measured using different heating and cooling rates; the results showed good agreement between both techniques, and in these studies was found that austenitic transformation is strongly dependent on the heating rate during continuous heating. The α–γ transformation enthalpy for this steel was about 17 J g−1. Microstructure was analyzed by optical and scanning electron microscope, and in the results can be observed that this steel has a martensitic structure with Mo- and Nb-rich carbides.