We elucidated the distance-dependent plasmonic effects on radiative transitions from an Eu(3+) ion-doped phosphor by varying the thickness of the dielectric spacer. Magnesium oxide prepared by electron-beam evaporation was chosen for the dielectric spacer. Spectral overlap between emission from Eu(3+) ions and the plasmon band of Ag nanoparticles led to improved luminescence intensity. This luminous enhancement was effective within the area of influence by localized surface plasmon resonance. At a long distance, the plasmon-enhanced luminescence was not effective. In addition, the numerical analysis results were in good agreement with the distance-dependent decay characteristics of plasmon resonance.