A new procedure is introduced to a differential adsorption bed (DAB) to determine the intrinsic concentration dependence of the surface diffusivity of hydrocarbons in activated carbon. The DAB is operated under a small change in bulk concentration that the adsorbed concentration is nearly constant during the adsorption process. The intrinsic surface diffusivity is then determined by analysing the experimental data using a pore and surface diffusion model. Experimental results show a much stronger concentration dependence of the surface diffusivity than that predicted by a Darken relationship in the studies of ethane and propane adsorption in Ajax-activated carbon. The effect of adsorption equilibrium equations on the prediction of the intrinsic surface diffusivity is also studied.