X-ray diffraction, calorimetry, vibrational and impedance spectroscopy studies of a new protonic conductor with the RbH(SO4)(0.81)(SeO4)(0.19) composition are offered. Crystals of this composition undergo five phase transitions at T = 245, 288, 353, 380 and 482K. The transition at 380 K is a superionic-protonic transition (SPT) related to a rapid [HS(Se)O-4(-)]reorientation and fast H+ diffusion. A sudden jump in the temperature dependance of conductivity confirms the presence of this transition. Above 380 K, this high temperature phase is characterized by a high electrical conductivity (10(-3)Omega(-1) cm(-1)) and low activation energy (E-a < 0.3 eV).