NOVELTY - A supported polymetallic nanoparticle is made by contacting a support with a polymetallic precursor comprising at least two metals and metal-ligand-metal group(s); and heating the support in the absence of oxidizing agent to form a supported polymetallic nanoparticle with an atomic ratio of the two metals approximately equal to a stoichiometric ratio of the metals in the polymeric precursor.    USE - For making nanocomposites for anode catalysts used in direct methanol fuel cells (DMFCs).    ADVANTAGE - The nanocomposites formed from the nanoparticles are commercially economical and provide desirable and controlled mixed metal nanocluster stoichiometries of at least 1:1 ratio.    DETAILED DESCRIPTION - Manufacture of supported polymetallic nanoparticles involves contacting a support with a polymetallic precursor comprising at least two metals and metal-ligand-metal group(s) of formula Mn-X-M'p; and heating the support in the absence of oxidizing agent to form a supported polymetallic nanoparticle comprising the two metals at a selected atomic ratio. The atomic ratio is approximately equal to a stoichiometric ratio of metals in the polymeric precursor.    M = atom of first metal;    X = halo, Hg, P, atom from Groups 14-17 of the Periodic Table, alkyl, alkenyl, alkynyl, aryl, aralkyl, alkylphosphino, arylphosphino, alkylsulfide, arylsulfide, alkylselenide, arylselenide, alkylmercuric, and arylmercuric, NH3, amine, alkene, heteroatomic aromatic molecules, arsenes and their derivatives;    M' = first or second metal; and    n and p = at least 1    X is a thermally degradable ligand having a degradation temperature lower than the degradation temperatures of M and M'.    INDEPENDENT CLAIMS are also included for the following:    (a) a polymetallic nanoparticle comprising at least two metals and metal-ligand-metal groups;    (b) a supported nanocomposite comprising a conductive support and polymetallic nanoparticles; and    (c) a method for making a metallic nanocomposite involving contacting a support with a metallic precursor comprising at least two metals and degradable ligand(s); and heating the support in the absence of oxidizing agent by microwave radiation to degrade the ligand(s).