Nanoparticles are known to affect the physical properties of bulk polymer materials. Here, we report the ability of metal nanoparticles, tailored with chemically matched short polymer ligands, to enhance interfacial properties, specifically the self-adhesion of a polymer melt. Gold nanoparticles functionalized with low-molecular weight (MW similar to 1500 g/mol) polystyrene ligands were introduced to the surface of a polystyrene film (MW similar to 278 kg/mol, PDI = 1.07). A second polystyrene film was brought into contact with the nanoparticle-decorated surface, and subsequently annealed. The resulting interface was characterized with the double cantilever beam (DCB) method to determine the critical strain energy release rate, G(c) of the welded interface as a function of nanoparticle surface coverage. The interfacial strength (G(c)) increased with nanoparticle area fraction until a maximum G(c) is achieved at an optimal value of nanoparticle coverage. The value of G(c) increased by approximately 100% relative to a sample without nanoparticles. This enhancement of interfacial adhesion reveals the potential for utilizing nanoparticles to improve mechanical properties of polymer interfaces.