NOVELTY - Preparing catalyst nanoparticles by cathodic reduction of oxygen and tolerant methanol, comprise preparing catalyst nanoparticles, preparing an electrochemical cell comprising a working electrode, a reference electrode and an auxiliary electrode, where an electrolytic solution comprises methanol and catalyst nanoparticles deposited on the surface of the working electrode in a density of 0.010-0.3 mg per cm2, measuring electrocatalytic activity of the electrochemical cell, and determining half-wave potential, residual recovery rate of the metal and molar ratio value of the catalyst.    USE - The catalyst nanoparticle is useful in a cathode for direct-methanol fuel cells, microfluidic cell, and microcell or nanopile in fuel (claimed), and in transport and in electric or portable electronic devices such as mobile phones.    ADVANTAGE - The nanoparticle: provides improved efficiency of energy conversion and reduced harmful emissions to the fuel cells; and can be easily prepared with improved electrocatalytic activity and stability on an industrial scale in an eco-friendly manner.    DETAILED DESCRIPTION - Preparing catalyst nanoparticles by cathodic reduction of oxygen and tolerant methanol, where the nanoparticles comprise a metal center comprising at least one supported or unsupported transition metal of platinum, ruthenium, palladium, rhodium or iridium, and sub-monolayer of a chalcogen comprising selenium or sulfur, where the molar ratio between chalcogen and transition metal, as maximum electrocatalytic activity, is less than 1, comprises: either preparing catalyst nanoparticles comprising supported or unsupported transition metal with sub-monolayer of the chalcogen in the molar ratio of less than or equal to 1, preparing an electrochemical cell comprising a working electrode, a reference electrode and an auxiliary electrode, where an electrolytic solution comprising methanol and catalyst nanoparticles deposited on the surface of the working electrode in a density of 0.010-0.3 mg per cm2, measuring electrocatalytic activity of the electrochemical cell by applying an oxidation potential of 0.8-1.4 V, under an inert atmosphere for 0-40 minutes, determining half-wave potential (E1/2) depending on the application time of the oxidation potential, determining residual recovery rate of the metal by the chalcogen for which the half-wave potential is maximum, and determining the molar ratio value of the catalyst; or preparing a mixture of the supported or unsupported transition metal and a mixture of water and isopropanol, under stirring, in a ratio of 2/1-10/1 for 5-60 minutes, adding an inorganic compound comprising a chalcogen in a molar ratio of less than or equal to 1, preferably 0.001-1, stirring at a temperature of 20-50 degrees C for 5-24 hours, preferably 10-20 hours, evaporating the water and isopropanol, calcining, under an inert atmosphere, at a temperature of 100-400 degrees C for 30 minutes to 2 hours. An INDEPENDENT CLAIM is included for the catalyst nanoparticles obtained by the process.