NOVELTY - Base metal-noble metal composite nanoparticles comprise nanoparticles consisting of noble metal(s), in a matrix of base metal. The base metal is a metal with larger ionization tendency than hydrogen.    USE - Base metal-noble metal composite nanoparticles are used in manufacture of catalyst particles for manufacture of catalyst (claimed) for electrode of polymer electrolyte fuel cell for motor vehicle.    ADVANTAGE - The base metal-noble metal composite nanoparticles are manufactured by simple process. The catalyst manufactured using the base metal-noble metal composite nanoparticles has high catalytic activity. Since the base metal shell portions are removable, the contamination of the noble metal nanoparticles is prevented. The noble metal nanoparticles have high dispersibility.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) manufacture of base metal-noble metal composite nanoparticles, which involves mixing a primary water phase containing base metal nanoparticles and a secondary water phase containing noble metal ion, forming nanoparticles which dissolves the base metal nanoparticles and depositing the base metal on the surface of the nanoparticles;    (2) manufacture of catalyst particles, which involves preparing the base metal-noble metal composite nanoparticles, supporting the base metal-noble metal composite nanoparticles using a support, and removing the base metal of the surface of the base metal-noble metal composite nanoparticles; and    (3) manufacture of electrode catalyst, which involves preparing base metal-noble metal composite nanoparticles, arranging the base metal-noble metal composite nanoparticles in at least one of the fuel electrode of the polymer electrolyte fuel cell, and an air electrode, removing the base metal of the surface of the base metal-noble metal composite nanoparticles by operating the fuel cell and exposing the base metal-noble metal composite nanoparticles to an acidic environment.