This paper introduces a simple, practical approach to measure the relative activity of various heterogeneous catalysts using electrical measurements. The applicability of this practical method was demonstrated on four commercial catalysts; a potassium-promoted iron oxide used for the dehydrogenation of ethyl benzene to produce styrene, a commercial hydrotreating catalyst used to remove sulfur and nitro gen from crude oil distillates such as gasoline or gas oil, a basic alumina that catalyzes the hydrolysis of halogenated hydrocarbons, and an unidentified catalyst from a major supplier. The electrical resistances of fresh, used and regenerated catalyst samples were measured on single particles, and specific conductivities were calculated. The difference between the conductivity of fresh and spent catalysts was found to be significant (1-5 orders of magnitude), while the conductivities of the regenerated samples were essentially identical to that of the fresh catalyst. Resistance measurements were also conducted in packed beds of the hydrotreating and basic alumina catalysts, and the concept of apparent specific conductivity was defined. The change in specific conductivity measured on single particles of fresh and regenerated catalysts, and the change in apparent specific conductivity measured in a packed bed of the same catalysts were very close. The simplicity of this new method renders it to be a potential sensitive on-line prediction method of relative catalyst activity.