The effect of fluid viscosity on the ohmic heating rates of fluid-particle mixtures was investigated. Fluids of identical electrical conductivity but different viscosity were used with identical amounts of solid particles (of electrical conductivity lower than the fluid) and heated ohmically in batch (static and vibrating), and continuous flow heaters. In the static ohmic heater the heating rate of the fluid and particles was found to be comparable for the different fluids. However; in the vibrating ohmic heater the heating rate of fluid and particles was found to increase with increasing fluid viscosity In the continuous flow ohmic heater; the mixture with the higher viscosity fluid heated faster than that with the lower viscosity fluid. The important implication is that poor interphase convective heat transfer may actually contribute to accelerated overall heating, since the more (electrically) conductive phase does not lose heat readily to the less (electrically) conductive phase, and consequently heats rapidly, transferring heat to the other phase by larger temperature differences.