Novel fine polymer particles containing ultrafine Pd, Pt or Rh metal dispersed on the core-shell [core, poly(styrene-co-acrylamide) or poly(styrene-co-acrylic acid); shell, LnPO(4)(Ln = Ce, Nd, Pr, Sm, La)] type microsphere were prepared by the emulsifier-free emulsion polymerization of styrene with acrylamide or acrylic acid followed by the addition of PdCl2, HPtCl6, or RhCl3 and finally by the addition of a mixture of Ln(NO3)(3) and NaH2PO4. Pyrolysis of the resulting polymer particles at 700-900 degrees C provides polymer-free hollow particles (diameter 450-550 nm) composed of noble metals and LnPO(4). The excellent catalytic reduction of NO gas into N-2 and O-2 was observed at 500-700 degrees C using the rersulting particles as catalyst.