The potentiometric properties of an epoxy resin-based anion-responsive polymer and its feasibility as a chloride sensing membrane are described. The response mechanism of the epoxy resin-based membrane is studied by varying the types and contents of epoxy components (e.g., resin, hardener, diluent, and plasticizer). It is found that epoxy resins cured with polyamine-type hardeners have excellent characteristics as chloride-sensing membranes, in terms of their selectivity, stability, sensor lifetime, and adhesion for constructing an all-solid-state sensing device. In addition, effects of the diluent or plasticizer added in an epoxy resin/hardener system on the potentiometric behaviors are investigated. To demonstrate the practical analytical utility of the epoxy resin-based electrodes, chloride levels in various controls and biological specimens (e.g., human sera and whole blood) are determined with a flow-cell system.