Ferroelectricity and large dielectric constant at room temperature have been demonstrated for cocrystals of phenazine and anilic acids constructing supramolecular assemblies. Deuteration of the anilic acids gives rise to an increase by more than 50 K in the transition temperature, which exceeds room temperature for the deuterated chloranilic acid. At room temperature in air, the crystals show a clear polarization hysteresis with a small coercive field. Application of hydrostatic pressure and halogen substitution in the anilic acids bring about the structural effect on the transition temperature in a parallel way, whereas the deuterium substitution does this in a distinct way. The observed large deuteration effect cannot be elucidated by the geometric change of the hydrogen bond, which has been considered as the possible mechanism of ferroelectricity in the conventional hydrogen-bonded with double-well potential.