A series of zirconium and titanium phosphate sulfophenylphosphonates of the type M(HPO4)(x)(O3PC6H4SO3H)(2-x) were prepared and characterized. They were found to exhibit proton conductivities which increased rapidly with increase in relative humidity (RH). At a RH of 85% and 25 degrees C conductivities of the order of 2.1-13 X 10(-2) Ohm(-1) cm(-1) were observed. At constant RH these compounds exhibit Arrhenius type behavior up to at least 100 degrees C. A new class of compounds of the type [M(HPO4)(x)(O3PC6H4SO3H)(2-x)][M’(HPO4)(x)(O3P-R-NH2)(2-x)], M = Ti, Zr, Th, has been prepared by self-assembly methods. These compounds also exhibit proton conductivities that rapidly increase with the RH. Their conductivities are one to two orders of magnitude less than the pure sulfophosphonates but they are much more stable to swelling in aqueous media. Their strong dependence on RH recommends them for use as humidity sensors.