Surface plasmon dispersion in nanoscale thin Ag films deposited onto the Ni(111) surface was investigated by angle‐resolved electron energy loss spectroscopy. We found that the dispersion curve contains only the quadratic term. The vanishing of the linear term was ascribed to the presence in the film of Ag 5sp‐related quantum well states. Screening effects enhanced by electron confinement in Ag quantum well states push the position of the centroid of the induced charge of the surface plasmon less inside the interface compared to other Ag systems, rendering null the linear coefficient of the dispersion curve. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)