The existing research on interface properties between heterogeneous materials mainly focuses on semiconductor-metal and dielectric materials, but little on organic-inorganic ones. In recent years, the nanoscale phenomena related to the mechanical properties of organic/inorganic material interfaces is gaining a lot of attention and becoming a new area of nanorelated research. Since gold (Au) exhibits excellent optical, electrical, and mechanical properties, it can be applied to nanooptics, mechanics, and electronics. This study explores the nano effect of the mechanical properties between the interface of Au and heterologous polymethyl methacrylate (PMMA) with different side groups, i.e., isotactic-PMMA, syndiotactic-PMMA, and atactic-PMMA. These heterologous PMMA thin films are prepared using a spin-coater to deposit the different side groups of PMMA upon Au thin film. A sputter technique is used to form Au thin films with different thicknesses. An indenter probe is applied by adding different forces on its tip into the PMMA and Au thin films to realize the interface mechanical properties such as hardness and Young's modulus. Finally, the time-dependent properties of viscoelastic materials are evaluated by using this harmonic nanoindentation test.