The inorganic-organic hybrid metal hydrogenophosphate with a formula of (C2H10N2)[Mn-2(HPO4)(3)](H2O) (1) shows layered crystal structure. The inorganic anion layer is built from Mn3O13 cluster units, and the interlayer spaces are filled by the charge-compensated ethylenediammonium dications together with the lattice water molecules. The thermogravimetry, variable-temperature powder X-ray diffraction, and the proton conductance under anhydrous and moisture environments were investigated for 1, disclosing that 1 shows high thermal stability and high proton transport nature, and the proton conductivity reaches to 1.64 x 10(-3) S.cm(-1) under 99% RH even at 293 K. The high proton conductivity is related to the formation of denser H-bond networks in the lattice.