NOVELTY - Electroconductive composite particles contain titanium oxide particles in which surface is coated with oxide fine particle layer, and phosphorus existing in the interface of titanium oxide particle surface and tin-oxide fine particle layer. The specific surface area of electroconductive composite particles is 2-20 times the specific surface area of titanium oxide particles, as measured by energy dispersive X-ray spectrometry of transmission-type electron microscope attachment.    USE - Electroconductive composite particles are used for composition for electrode catalyst layer for fuel cell (all claimed) e.g. polymer electrolyte fuel cell and direct-methanol fuel cell, and used as platinum nanoparticle catalyst carrier of air electrode catalyst layer.    ADVANTAGE - The electroconductive composite particles have high specific surface area, and favorable tolerance with respect to oxidation and strong acid, and provides electrode catalyst layer with reduced time-dependent changes and reliable fuel cell with excellent operability. Since phosphorus exists in the interface of titanium oxide particle surface and tin-oxide fine particle layer, the diffusion of titanium in titanium oxide particles to the tin-oxide fine particle layer is suppressed. The peeling of oxidation tin layer from a titanium oxide particle is suppressed.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) manufacture of electroconductive composite particles, which involves dripping an aqueous solution obtained by dissolving tin chloride in titanium oxide particles-containing dispersion liquid containing titanium oxide particles, dispersing agent containing phosphorus and water, depositing a coating layer which is the titanium oxide particle surface from hydroxylated tin, and heating titanium oxide particles deposited in the coating layer containing hydroxylated tin at 300-1000 degrees C;    (2) composition, which comprises the electroconductive composite particles and a dispersion medium of a fuel cell; and    (3) electrode catalyst layer, which comprises the electroconductive composite particles.