NOVELTY - The composite membrane (12) comprises an insulating substrate (14) having openings, a membrane electrode assembly disposed in each of the openings, and an insulating protective layer provided on a first catalyst layer side of the substrate and a second catalyst layer side of the substrate, where the protective layer is present in between the adjacent first and second catalyst layers and the second catalyst layer side is disposed counter to the first catalyst layer side. The membrane electrode has an electrolyte membrane (22) containing ionomer, and a first catalyst layer.    USE - The composite membrane is useful in a fuel cell (claimed), which is a planar fuel cell and is useful in space applications, automobiles, mobile devices such as cell phones, notebook-size personal computers, personal digital assistant, MP3 players, digital cameras, electronic dictionaries or electronic books and large and small scale power generation.    ADVANTAGE - The composite membrane can be economically manufactured with reduced size, and shows excellent ion conductivity in a moist or humidified conditions.    DETAILED DESCRIPTION - The composite membrane (12) comprises an insulating substrate (14) having openings, a membrane electrode assembly disposed in each of the openings, and an insulating protective layer provided on a first catalyst layer side of the substrate and a second catalyst layer side of the substrate, where the protective layer is present in between the adjacent first and second catalyst layers and the second catalyst layer side is disposed counter to the first catalyst layer side. The membrane electrode has an electrolyte membrane (22) containing ionomer, a first catalyst layer provided on one face of the electrolyte membrane, and a second catalyst layer provided on the other face of the electrolyte membrane. The protective layer contains a resin whose number of C-F bonds is greater than that of the substrate, and is made of a resin for which the transmission factor of laser beams used for microfabrication of the catalyst layers is less than or equal to 23%. An INDEPENDENT CLAIM is included for a method for fabricating a composite membrane for a fuel cell.    DESCRIPTION OF DRAWING(S) - The diagram shows a cross-sectional view of a structure of a composite membrane for a fuel cell.    Composite membrane (12)    Substrate (14)    Interconnector (18)    Electrolyte membrane (22)    Cathode catalyst layer. (24)