A proton conducting titanate includes titanate and a sulfonic acid group-containing moiety having proton conductivity introduced into the surface of the titanate, in which the sulfonic acid group-containing moiety is directly bound to the titanate via an ether bond (—O). A polymer nano-composite membrane includes the proton conducting titanate, and a fuel cell includes the polymer nano-composite membrane. The proton conducting titanate is provided with a sulfonic acid functional group having proton conductivity, which increases the proton conductivity of the polymer nano-composite membrane. The polymer nano-composite membrane includes the proton conducting titanate, and thus can have a controllable degree of swelling in a methanol solution, and the transmittance of the polymer nano-composite membrane can be reduced. The polymer nano-composite membrane can be used as a proton conducting membrane in fuel cells to improve the thermal stability, energy density, and fuel efficiency of the fuel cells.