There are provided a surface modified material comprising a base material, and one or more kinds of sulfonimide compound groups bonded onto the surface of the base material via one or more linking groups -A-Y′— (A is a direct bond or an organic group. Y′ is a bonding site with the base material.); the sulfonimide compound group comprising, in its molecular structure, one or more linking groups -A-Y′— and two or more sulfonimide groups; as well as a fuel cell using the surface modified material for a catalyst layer. There is also provided a sulfonimide compound for surface modification comprising one or more reactive end groups -A-Y (A is a direct bond or an organic group. Y is a reactive functional group.) and two or more sulfonimide groups.