An enhancement in proton conductivity for poly(aspartic acid)/sodium polyaspartate (P-Asp) by synthesizing thin film on MgO substrate was investigated. The average degrees of polymerization and molecular weight were ̃70 and ̃9400, respectively. The degree of protonation in the carboxylic acid groups was 10 %. The proton conductivities of the pelletized P-Asp and thin film were 6.4 x 10-4 and 3.4 x 10-3 S cm-1, respectively, under a relative humidity of 70 % and 298 K. The proton conductivity of the thin film was found to be five times higher than that of the pelletized P-Asp. The activation energy for the proton conduction of the pelletized P-Asp was 0.89 eV. The activation energy of P-Asp thin film was smaller than that of the pelletized sample. Application of this phenomenon may lead to a new method for producing highly proton-conductive material.