An investigation is reported on the coating of ZnS:Cu,Cl phosphors by $HfO_2$ using atomic layer deposition method. Hafnium oxide films were prepared at the chamber temperature of $280^{circ}C$ using $Hf[N(CH_3)_2]_4;and;O_2$ as precursors and reactant gas, respectively. XPS and ICP-MS analysis showed the surface composition of coated phosphor powder was hafnium oxide. In FE-SEM analysis, the surface morphology of uncoated phosphors became smoother and clearer as the number of ALD cycle increased from 900 to 1800. The photoluminescence intensity for coated phosphors showed $7.3{sim}13.4%$ higher than that of uncoated. The effect means that the reactive surface is uniformly coated with stable hafnium oxide to reduce the dead surface layer without change of bulk properties and also its absorptance is almost negligible due to ultrathin(nano-scaled) films. The growth rate is about $1.1{AA}/cycle$.