Degradation due to electron beam irradiation is a significant problem for ZnS based phosphors, particularly for flat panel displays. In this study, ZnS:Ag phosphor particles were coated by nanoparticles of ZnO:Al by pulsed laser deposition (PLD), to suppress the cathodoluminescence (CL) degradation process under electron bombardment at 15 k V. The pressure of the vacuum chamber and the deposition time were changed to control the morphology of the coating, i.e. thickness, continuity, and uniformity. CL degradation of the phosphors was slowed down for all cases by the nanocoating. The relationship between the CL degradation and the morphology of the coating material was examined by an SEM combined with a simultaneous CL measurement device. Degradation mechanisms were elucidated in terms of the morphology of the coating material and the change in the surface atomic species during irradiation of the electron beam.