The formation of metallic layers on ultrathin molecular films via a well-controlled interface is essential for constructing organic nanodevices composed of metal/molecule/metal sandwich junctions. The scanning tunneling microscopy and spectroscopy studies demonstrate that an ultrasharp metal/molecule interface is realizable by depositing size-selected Ag nanoclusters (Ag-n) from the gas phase on few-layer films of C-60 molecules. It is also demonstrated that Ag-n nanoclusters can be immobilized on monolayer films of oligothiophene molecules via C-60 molecules, although they three-dimensionally aggregate on bare oligothiophene films. It is also shown that electrons and holes are injected into the topmost layer of C-60 films via the Ag-n/C-60 interface. Moreover, the barrier height for carrier injection at the Ag-n/C-60 interface can be modified depending on the size of Ag-n nanoclusters and the kinetic energy during the deposition. The present results demonstrate that the controlled immobilization of metallic nanoclusters on molecular films can be used as a fabrication technology for metal/molecule/metal junctions.