Catalytic hydrogen evolution from neat tetrahydronaphthalene occurs under normal liquid-phase conditions effectively, using palladium catalysts supported on activated carbon fibers (ACFs). ACFs that have relatively high surface areas seem to be suitable for use as supports. Although the co-product, naphthalene, accumulated in the reaction system retards the reaction, it can be removed. easily, so that the initial catalyst activity recovers almost completely. Thus, the catalysts stably exhibit high activity in the reuse cycles at least five times.