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The present work was focused to study nanomechanical properties of ZnO thin films deposited on different substrates (Corning Glass and Fused Quartz) using DC-sputtering. The crystallinity and microstructure are correlated with process conditions and post annealing treatment in NH3 environment, which in turn affects the mechanical performance. The structural growth accompanied a change in crystalline nature and microstructure as the substrate is altered from corning glass substrate to fused quartz at similar synthesis conditions. The post deposition annealed ZnO thin films demonstrated agglomerated particles with no clear grain boundaries having nano-cracks present in the morphology, which is attributed as NH3 effect on microstructure. The mechanical properties such as hardness (6.89-7.76 GPa), Young's modulus (94.9-124.6 GPa), and coefficient of friction ̴ (1.0-3.0) of ZnO thin films were measured using three sided pyramidal Berkovich nanoindentation. Load-unload segment of indentation curve of thin films which is measured at continuous loading revealed no event of discontinuity (≥ 2 nm) during loading/unloading, indicating no fracture or delamination during indentation. The critical load of ZnO thin films failure was analysed using scratch testing ramp loading and the value of critical load was found around ̴ 535.6 µN to ̴ 668.4 µN.