Dielectric investigations in the temperature and frequency ranges 150-450 K and 10(2)-10(5) Hz, respectively show that Rb-0.6(NH4)(0.4)HSO4 composition is ferroelectric below T-c = 290 K. A.C. complex impedance measurements were performed on this ferroelectric and superconductor material at high temperatures. An impedance relaxation was observed. In addition, to the ferroelectric properties, an important level of conductivity at high temperatures attributed to the motion of H+ proton at least in the off-stoichiometric material, was observed. This behavior indicates the presence of superionic protonic phase transition in this material.