We report on photoinduced fluorescence enhancement (PFE) in a thin film of CdSe/ZnS core/shell quantum dots (QDs) sandwiched between a glass substrate and a silicon oxide layer and the dependence on the degree of proximity between the QDs. CdSe/ZnS QDs capped with tri-n-octylphosphine oxide (TOPO) were colloid-chemically synthesized, and the QD thin films of various thicknesses were then fabricated on glass substrates using a spin-coating technique. A SiOx protective layer was subsequently sputtered on the QD thin film to prevent photoadsorption of water molecules and photooxidation. The fluorescence intensity monotonically increased under continuous excitation except for the case of the thinnest sample which exhibited intensity decay. Interestingly, the increasing rate of fluorescence intensity increases as a function of the number of QD layers, θ, to the extent of θ ≤ 3.2 and then decreases at θ ≥ 3.2. Fluorescence lifetime measurements indicate that the band-edge radiative relaxation probability become...