Ellipsometric parameters of layer-by-layer self-assembled osmium complex-derivatized poly(allylamine) and glucose oxidase multilayers, (PAH-Os)(n)(GOX)(n), were measured at different wavelengths during oxidation-reduction cycles. Data were analyzed using an isotropic single layer model for the enzyme films. The changes in film thickness and refractive index during cyclic voltammetry and potential square wave experiments arise from redox modulation causing film swelling due to the exchange of anions and solvent with the bathing electrolyte. These changes correlate well with the fraction of oxidized PAH-Os(III) in the film.