▎ 摘　　要

NOVELTY - A solid acid contains oxidation graphite and/or oxidation graphene with thickness of not greater than 10 nm which is sulfonated. USE - A solid acid used for solid acid catalyst and proton conducting membrane (claimed). ADVANTAGE - The solid acid is excellent in handleability, proton electroconductivity, and function as acidic catalyst. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for: (1) a solid acid catalyst comprising solid acid; (2) a proton conducting membrane comprising solid acid; and (3) a manufacturing method of solid acid involving oxidizing graphite and obtaining oxidation graphite, sulfonating oxidation graphite after peeling in layer direction.