We present a description of surface plasmon resonance (SPR) with quantum dynamical simulations based on the path integral method. SPR represents the excitation of surface plasmons (SPs), i.e., collective oscillations of conduction electrons in a metal film, usually created by the plane-polarized visible light. In the classical description, the momentum matching between incident photons and SPs allows the energy of the incident photons to be absorbed into exciting SPs and to form evanescent waves on the metallic thin film surface. While SPR has been understood through classical approaches using Maxwell's equations, extremely small nanoparticles coupled with SPs induces electromagnetic field enhancement often called localized SPR (LSPR) that is classically not well understood. Use of such nanoparticles smaller than a few nanometers in size has made it imperative to consider quantum effects such as quantum size effect. We present a hybridized model to describe SPR/LSPR using quantum states that interact with a dissipative medium according to size-dependent absorption spectra of nanoparticles.