Cation transport through a cellulose acetate-poly(N,N-dimethylaminoethyl methacrylate) membrane (CA:PDMAEMA) was studied with scanning electrochemical microscope (SECM) and the thickness increase of the membrane was monitored with ellipsometry. Upon addition of the polyelectrolyte PDMAEMA, the permeability of the probe cation (ferrocenium methanol, FcMeOH) was increased as much as 40-fold. Soaking membranes in an electrolyte solution doubled the permeability in plain CA membranes, whereas for PDMAEMA containing membranes the opposite was observed and the permeability was reduced by 20-40%. This time-dependent behavior is shown to be a result of the presence of PDMAEMA within the membrane matrix, thus providing an interesting platform for controllable membrane permeability. (c) The Author(s) 2018. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License.