Electroless Cu coating of zirconia particles using a Pdo catalyst is investigated in this paper. Uncoated and Cu-coated ZrO2 particles are characterized by various analytical techniques to understand the mechanism of electroless Cu coating of ZrO2 particles, which involves reduction of Pd2+ on ZrO2 particle surfaces by Sn2+ to produce pure metallic Pdo clusters, which provide catalytic sites for Cu deposition. The concept of XPS core-level binding energy shift due to small cluster size is utilized to predict the size of pure Pdo clusters.. The electroless Cu-coating process can be utilized in the future to produce Cu-doped ZrO particles required for various potential applications.