ZrN films were prepared using microwave electron cyclotron resonance (MW-ECR) plasma enhanced unbalanced magnetron sputtering (PE-UMS) technique. The plasma characteristics near the holder were diagnosed by Langmuir probe for various depo sition conditions and the films obtained were characterized by electron probe mi croanalysis x-ray diffraction and micro-hardness. As the N2 flow rate increas es from 2 to 20sccm, the ion density initially increases from 807×109 to 8 31×109cm-3 and then decreases to 752×109c m-3, while the N +2 ion density increases monotonically from 312×10 -8 to 335×109cm-3 and the electron temperature does not va ry much. The N concentration in t he films increases and the grain size decreases as the N+2 ion density increases. And the films become more and more amorphous as the N/Zr ratio is above 1 4 The corresponding microhardness of the deposited films increases from 22 5GPa to the maximum of 2678GPa, and then decreases linearly to 1982GPa as th e N2 flow rate increases from 8 to 14sccm. The mechanism of the influ ence of t he plasma characteristics on the microstructure and mechanical properties of the deposited films were discussed.