We have studied the surface-smoothing effect of an ultrathin germanium (Ge) layer on silver (Ag)-silica (SiO2) nanocomposite films for superlensing applications. Our experimental results indicate that inserting a thin Ge layer below the silver-silica composite films can reduce the final surface root-mean-squared (RMS) roughness to under 1 nm. Additionally, the metal nanostructure plays a role in both the smoothing effect and the optical properties of the nanocomposite films. Our experimental results show that the Bruggeman effective medium theory (EMT) is not sufficiently accurate to describe some properties of our nanocomposite films. In addition to the constituent materials and their filling fraction within the composites, the detailed geometries of the metal nanostructures also show a significant influence on the optical properties of the composite films. This influence has not been taken into account by the EMT formulation. X Z (b) without a Ge sub-layer X Z (a) with a Ge sub-layer Surface morphologies from AFM topographs (a) 5 nm SiO 2 / 5 nm Ag composite film on a Ge/SiO 2 /Si(100) substrate. (b) The same composite layers on a SiO2/Si(100) substrate. The composite film (a) with a Ge sub-layer under it is smoother than the composite film (b) without a Ge sub-layer