NOVELTY - A modified material is obtained by subjecting a mixture of a nitrogen-containing electroconductive carbon and a metal complex to modification treatment chosen from heat-processing, radiation irradiation treatment, and electrodischarge treatment. The nitrogen-containing electroconductive carbon is obtained by reacting a functional group or a multiple bond in an electroconductive carbon with a nitrogen-containing compound.    USE - Modified material is used in catalyst compositions used for electrode catalysts of membrane-electrode assemblies of fuel cells (all claimed) e.g. polymer electrolyte type fuel cells used in mobile telephones, motor vehicles, domestic power supplies, and portable personal computers. Can also be used for deterioration inhibiting agent of ion-conductive films used in water electrolysis, desulfurization and nitrogen-oxide-removal catalyst, oxidation-reduction catalyst layers of dye-sensitized solar cells, carbon-dioxide reduction catalysts, modification hydrogen-production catalyst, oxygen sensors, pharmaceuticals and agrochemicals, and antioxidants of foodstuffs.    ADVANTAGE - The modified material exhibits excellent redox activity in a redox reaction accompanied by the transfer of electrodes and hence can be used suitably as a material for forming electrode catalyst of fuel cell.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) catalyst composition containing the modified material;    (2) membrane-electrode assembly (20) consisting of catalyst layers (14a,14b) containing an electrode catalyst containing the catalyst composition on both sides of an electrolytic membrane (12); and    (3) nitrogen-containing electroconductive carbon obtained by mixing an aldehyde, N-monosubstituted- alpha -amino acid, and electroconductive carbon, and heating the mixture at 80-300 degrees C.    DESCRIPTION OF DRAWING(S) - The drawing shows a longitudinal cross-sectional view of the fuel cell.    Fuel cell (10)    Electrolytic membrane (12)    Catalyst layers (14a,14b)    Gas-diffusion layers (16a,16b)    Membrane-electrode assembly (20)