W-N and Ta-N coatings were manufactured using r.f. reactive magnetron sputtering technique in mixed atmosphere of Ar+N 2. The effect of sputtering power on the microstructure and mechanical properties of these coatings has been investigated. It was found that increasing sputtering power induced structure transformation of W-N and Ta-N coatings from hexagonal WN to fcc ω-W2N and from fcc TaN through a mixture of orthorhombic Ta3N5 and fcc TaN to orthorhombic Ta3N5, respectively. The increase in sputtering power led to grain refinement which played a major role in hardness enhancement. At the highest sputtering power of 100W, the average grain size of Ta-N and W-N coatings reduced to minimum value of 7 nm and 21 nm, correspondingly the hardness reached maximum value of 29 GPa and 31 GPa, respectively. However, Ta-N and W-N coatings possessed the biggest adhesion strength of ̃41 N and ̃48 N at the lowest sputtering power of 40 W and 25 W, respectively.