Incorporating nanoparticles (NPs) within a polymer host to create polymer nanocomposites (PNCs) while having the effect of increasing the functionality (e.g., sensing, energy conversion) of these materials influences other properties. One challenge is to understand the effects of nanoparticles on the viscosity of nanoscale thick polymer films. A new mechanism that contributes to an enhancement of the viscosity of nanoscale thick polymer/nanoparticle films is identified. We show that while the viscosities of neat homopolymer poly(2-vinylpyridine) (P2VP) films as thin as 50 nm remained the same as the bulk, polymer/nanoparticle films containing P2VP brush-coated gold NPs, spaced 50 Mm apart, exhibited unprecedented increases in viscosities of over an order of magnitude. For thicker films or more widely separated NPs, the chain dynamics and viscosities were comparable to the bulk values. These results-NP proximities and suppression of their dynamics-suggest a new mechanism by which the viscosities of polymeric liquids could be controlled for nanoscale applications.