Multilayer films with anionic phosphomolybidic acid (PMo12) clusters have been fabricated via the electrostatic layer-by-layer (LbL) method The charged mass transport phenomena of these thin films have been studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) with [Fe(CN)(6)](3-/4-) and [Ru(NH3)(6)](3+/2+) as the redox probes By adding a film resistance and a film capacitance to the conventional Randles equivalent circuit we can calculate the diffusion coefficient values that help understand the microscopic nature of the thin films When the negatively charged probe [Fe(CN)(6)](3-/4-) was used lower diffusion coefficients were obtained for multilayers deposited from higher ionic strength solutions This relationship was less obvious when the positively charged probe [Ru(NH3)(6)](3+/2+) was used in which the electrostatic attraction between PMo12 clusters and the probe ions complicates the mass-transfer process It is believed that the addition of salt to dipping solutions increases the tortuosity of the films so the mass transport takes longer paths inducing lower diffusion coefficients Higher PMo12 loading causes lower diffusion coefficients due to the polyoxometalate clusters blocking the paths for charged probe ions