Thermal stability and mechanical properties of zirconium tungsten nitride (Zr-W-N) thin films have been studied. Nano–structured Zr-W-N thin films have been deposited on Si (100) substrates by reactive magnetron sputtering at varying substrate temperatures Ts (1000-600 °C). For 100 °C ≤ Ts ≤ 600 °C, X-ray diffraction patterns of the films show a crystalline fcc phase with (111) and (200) preferred crystallographic orientations of grains. Maximum wear resistance (H/Er ~ 0.22) and maximum resistance to fatigue fracture (H3/Er2 ~ 1.0 GPa) have been obtained for the film deposited at Ts = 400 °C. Post annealing of the films deposited at 400 °C have been carried out in air from 1000-600 °C. Oxygen starts to be incorporated at 300 °C and films begin to peel-off above 400 °C due to increase in oxygen incorporation. Hardness and elastic modulus of annealed films increase with increasing strain.