The pressure effect on phase transitions and protonic conductivity in Rb3H(SeO4)(2) and (NH4)(3)H(SO4)(2) was studied at P less than or equal to 2.0 GPa, 300 K less than or equal to T less than or equal to 500 K. The temperature of the superprotonic transition in both crystals decreases with pressure at P less than or equal to 1.0 GPa. New phases originate in Rb3H(SeO4)(2) at P greater than or equal to 1.22 GPa and in (NH4)(3)H(SO4)(2) at P greater than or equal to 1.02 GPa. The activation volumes for low- and high-conductivity phases were calculated from baric dependencies of protonic conductivity.