Nanoparticles (NPs) are currently receiving considerable attention for medical and dental applications, but their biological effects have not yet been fully elucidated. This study evaluated the MMP inhibition of gold (AuNPs) and platinum nanoparticles (PtNPs) stabilized by polyvinylpyrrolidone and their toxic effects on murine macrophages (RAW264). While both NPs inhibited MMP-8, 9, the AuNPs demonstrated no cytotoxicity at all concentrations tested. It was suggested that AuNPs are promising for application to dental materials without causing any cytotoxicity and inflammatory response.