Abstract: The aim of this study is to investigate magnetic properties of an example of half-metallic and ferromagnetic compounds, namely, the half Heusler PtMnSb. From the magnetic measurements, it can be shown a change from a localized magnetism due to the spin waves thermally excited, to an itinerant magnetism with spin fluctuations is to reduce the moments in this compound. Furthermore, the electrical and thermal resistivity measurements were performed. The resistivity results with respect to the magnetic properties are confirmed and a transition of a half-metallic state to a metallic state at 100 K is observed.