Blue-emitting ZnS:Ag phosphors were coated with nanoscale zinc oxide (ZnO) and Al-doped ZnO (AZO) and the cathodoluminescence (CL) performance of the coated phosphors was investigated. The nanoscale coating was obtained by controlling the hydrolysis reaction of ZnCl2 alcoholic solution using diethylamine as a gradual OH- former, and Al doping was performed to increase the electrical conductivity of ZnO. The coatings were composed of either nanosized particles or a continuous nano layer, and the AZO-coated phosphor had a more uniformly covered surface. The coated phosphors exhibited improved aging behavior under CL excitation and the AZO coating was more effective at suppressing the degradation, possibly due to its uniformity and high conductivity.