The CrTiAlN and CrTiAlSiN thin films with various silicon contents were fabricated by a magnetron co-sputtering process. The influences of silicon contents on the microstructure, mechanical and tribological properties of CrTiAlSiN films were investigated in this work. The crystal structures of CrTiAlN and CfriAlSiN had face-centered cubic structure. The microstructure of the CrTiAlSiN thin films changed from a columnar structure to a dense and compact morphology as the silicon content increased from 0.4 at.% to 2.9 at.%. A nanocomposite microstructure with nanogtains around 5 nm in diameter was achieved for the coating containing 8.0 at.% Si. A maximum hardness of CrTiAlSiN around 34 GPa were achieved through a proper adjustment of Si content (similar to 1.0 at%). An excellent indentation toughness, Kc, 1.89 MPa root m was obtained when the Si content was 1.6 at.%. The wear resistance of coating was significantly improved as the hardness increased. In this work, the relationship among the hardness, plastic deformation resistance, toughness, tribological properties and Si content was discovered for the CrTiAlSiN coating. (C) 2017 Elsevier B.V. All rights reserved.