NOVELTY - Proton-conductive composite electrolyte membrane contains metallic compound particles having proton conductivity, organic macromolecular material (11) having proton conductivity and dispersing agent having sulfonic acid group. The metallic compound particles have average primary particle diameter of 0.5-5 nm, average secondary particle diameter of 50 nm or less and mean dispersion particle diameter of 30 nm or less. The content of metallic compound particles is 30-60 wt.% with respect to total weight of electrolytic membrane.    USE - Proton-conductive composite electrolyte membrane is used for membrane electrode assembly for fuel cell (both claimed) e.g. direct methanol fuel cell and polymer electrolyte fuel cell used as power supply for portable electronic device.    ADVANTAGE - The composite electrolyte membrane has excellent proton conductivity, and reduced fuel penetration property.    DETAILED DESCRIPTION - Proton-conductive composite electrolyte membrane contains metallic compound particles having proton conductivity, organic macromolecular material having proton conductivity and dispersing agent having sulfonic acid group. The metallic compound particles have average primary particle diameter of 0.5-5 nm, average secondary particle diameter of 50 nm or less and mean-dispersion particle diameter of 30 nm or less. The content of metallic compound particles is 30-60 wt.% with respect to total weight of electrolytic membrane. The weight ratio of dispersing agent and metallic compound particles is 0.1:100-5:100. An INDEPENDENT CLAIM is included for membrane electrode assembly, which includes proton-conductive composite electrolyte between oxygen electrode containing catalyst layer which reduces oxygen and fuel electrode containing catalyst layer which oxidizes fuel.    DESCRIPTION OF DRAWING(S) - The drawing shows schematic view of metallic compound particles in dispersion state.    Organic macromolecular material (11)    Metallic compound aggregate (12)