Titanium nitride is a ceramic coating where titanium and nitrogen form a crystalline compound with a face-centered cubic structure that has a relatively high hardness (25 GPa) and good adhesion on many substrates. However, temperature stability is limited to about 500 °C. Among the elements to improve this property (like Al, Si, ..) it was decided to study the influence of hafnium. Ti-Hf-N thin films were deposited on Si substrates by reactive co-sputtering with a fixed power on the Ti target and variable power on the Hf target. This led to the formation of TixHf1-xN single-phase coating with a variable composition. The Hf /(Ti + Hf) ratio was varied between 0.23 and 0.70. When the titanium is substituted by the hafnium, the conical columnar microstructure is replaced by a dense and amorphous-like microstructure. The maximum hardness (30 GPa) is reached for a ratio Hf / (Ti + Hf) = 0.51.