Abstract: Here the microstructures and the mechanical properties of RF magnetron sputtering ZnO thin film on silicon substrates annealed at different temperatures were investigated by XRD,AFM and nanoindentaion.The effects of annealing temperature on the microstructures and mechanical properties were discussed.As the annealing temperature increased from room temperature（RT） to 650℃,both the（002） orientation degree of the ZnO film and the grain size increased.Due to the grain size effect,hardness of the ZnO film increased from 2.5 to 5.5GPa which the annealing temperature increased from RT to 450℃,and then dropped from 5.5 to 4.2GPa which the annealing temperature increased from 450 to 650℃.Young’s modulus didn’t show a clear trend for the combined effect of grain size and film orientation.The highest and lowest Young’s modulus was 26.7GPa and 21.5GPa,appearing in the sample annealed at 450℃ and 200℃ respectively.Results show that proper anneal treatment can improve the crystal quality and enhance the mechanical properties of the ZnO film.