NOVELTY - Preparation of noble metal-titanium dioxide nano composite particles involves dissolving emulsifier (E1) having low hydrophilic-lipophilic balance value in non-polar solvent to obtain solution (A), dissolving noble metal salt in polar solvent, adding solution (A) in obtained noble metal solution, and homogenizing to obtain fine emulsion, adding titanium-containing precursor into fine emulsion, mixing, reacting resultant mixture, then adding liquid reducing agent, mixing, reacting the resultant mixture at 20-60 degrees C for 1-48 hours, and centrifugally separating obtained mixture.    USE - Preparation of noble metal-titanium dioxide nano composite particles used as photocatalyst (all claimed) used in decomposition of water, organic wastewater treatment, photocatalytic organic reaction and solar cell.    ADVANTAGE - The method enables preparation of noble metal-titanium dioxide nano composite particles with high catalytic activity.    DETAILED DESCRIPTION - Preparation of noble metal-titanium dioxide nano composite particles involves dissolving emulsifier (E1) having low hydrophilic-lipophilic balance value in non-polar solvent to obtain solution (A), dissolving noble metal salt in polar solvent, adding solution (A) in obtained noble metal solution, and homogenizing to obtain fine emulsion, adding titanium-containing precursor into fine emulsion, mixing, reacting resultant mixture at 40-160 degrees C for 10 minutes to 12 hours, then adding liquid reducing agent into obtained noble metal salt-titanium oxide composite nanoparticle dispersion liquid, mixing, reacting the resultant mixture at 20-60 degrees C for 1-48 hours, and centrifugally separating obtained mixture. The emulsifier (E1) is chosen from Span (RTM: emulsifier), Tween (RTM: emulsifier), OP-10-type emulsifier and block copolymer-type emulsifier. The non-polar solvent is chosen from 6-20C aliphatic hydrocarbon, 6-20C cycloalkane, and 1-4C alkyl benzene. The content of emulsifier (E1) is 0.1-20 %mass with respect to non-polar solvent. The noble metal salt is chosen from chloroauric acid, chloroplatinic acid, noble metal nitrate and/or noble metal tetrafluoroborate. The polar solvent is water or mixture of water and organic solvent. The organic solvent is chosen from methanol, ethylene glycol, dimethyl sulfoxide, dimethyl formamide and/or tetrahydrofuran. The titanium-containing precursor is of formula: R3O-Ti(-OR2)(-OR4)-OR1 or Cl-Ti(-Cl)(-Cl)-Cl. The reducing agent comprises 40-80 %mass hydrazine hydrate solution, 1-5C primary amine, 1-5C secondary amine and/or 2-8C diamine. The ratio of polar solvent and titanium-containing precursor is 0.5-5:1. The mass ratio of non-polar solvent and polar solvent is 2-50:1. The amount of noble metal salt is 0.05-50 %mass with respect to the amount of titanium-containing precursor. The ratio of reducing agent and noble metal salt is 1-100:1.    R1-R4=1-5C alkyl.