A proton conducting membrane comprising, as a main component, a ceramic structure in which an oxygen atom of a metal oxide is bonded through the oxygen atom with at least one group derived an oxygen acid selected from —B(O)3—, —S(═O)2(O)2—, —P(═O)(O)3—, —C(═O)(O)2—, and —N(O)3—, wherein the metal oxide and said at least one group derived from the oxygen acid share the oxygen atom, the proton conducting membrane being made by a sol-gel reaction of the oxygen acid or its precursor and a precursor of the metal oxide in order to obtain a sol-gel reaction product, followed by heating of the sol-gel reaction product at a temperature in a range of 100° C. to 600° C., the oxygen acid or its precursor being selected from a boric acid, a sulfuric acid, a phosphoric acid, a carbonic acid, a nitric acid, and precursors thereof. Thus, a novel proton conducting membrane is provided.