PROBLEM TO BE SOLVED: To provide a platinum nanoparticle dispersion which has excellent permeability and wettability to filters composed of hydrophobic fibers and allows wide and uniform support of platinum nanoparticles on fiber and other claims.SOLUTION: A platinum nanoparticle dispersion contains 0.01-1 mass% of one or more selected from sulfosuccinic acid bisalkyl ester salts, alkyl sulfates, alkyl naphthalene sulfonates, benzethonium chloride and polyoxyalkylene alkyl ethers of an HLB of 10-20 and 0.01-25 mM of platinum nanoparticles.