Properties of the proton transfer in (KDP) are examined on the basis of a model that was proposed to explain the mechanism of the phase transition from a ferroelectric phase to a paraelectric phase; it is found that, in the paraelectric phase, a proton transfers from one site to the other site at a jump rate of the order of . Scattering functions for incoherent scattering of thermal neutrons induced by the proton motion are also calculated in the framework of the classical approximation.