The effect of microstructure on thermal stability and mechanical properties of co-sputtered deposited Zr–W–B–N thin films on Si (100) substrates have been studied in detail. The power density of boron target has been varied from 0.1 to 7.5 W/cm 2 to obtained films of varying microstructure. Electron microscopy, X-ray diffraction analysis , atomic force microscopy, Raman scattering spectra, nano and micro indentations were used to investigate the interrelations between the microstructure and the variations in strength properties of nanocomposite Zr–W–B– N thin films. It has been observed that films with boron content b 2.3 at.% exhibited (200) preferred crystallographic orientation of grains and columnar structure. While the films of boron content ≥7.5 at.% are columnarless with crystal phase grain size less than 7 nm and of amorphous-crystalline structure. The film with boron concentration ~7.5 at.% exhibits maximum hardness (~37 GPa), wear resistance (H/E r ~ 0.24) and fracture toughness (2.9 MPa·m 1/2). Post annealing of the film with ~7.5 at.% boron concentration has been carried out in vacuum (T v) and air (T n) up to 900 °C. Zr–W–B(7.5 at.%)–N film retains its fcc structure during vacuum annealing up to 900 °C. Oxygen starts to incorporate at T n = 500 °C and its percentage goes up with increasing T n up to 900 °C.