In this report, we describe a novel approach to create an electrochemical gating system using mixed polymer brushes grafted to an electrode surface, and we explore the switchable properties of these mixed polymer brushes. The morphological transitions in the mixed polymer brushes associated with the electrode surface result in the opening, closing, or precise tuning of their permeability for ion transport through the channels formed in the nanostructured thin film in response to an external stimulus (pH change). The gating mechanism was studied by atomic force microscopy, ellipsometry, contact angle measurements, force-distance measurements, and electrochemical impedance spectroscopy. In comparison to a homopolymer brush system, the mixed brush demonstrates much broader variation of ion transport through the thin film. We suggest that this approach could find important applications in electrochemical sensors and devices with tunable/switchable access to the electrode surface.