An ion-selective membrane based on a polyimide polymeric matrix plasticized with diethylene glycol dibenzoate and containing calcium synthetic ionophores was used to obtain a potentiometric Ca²⁺ sensor. It gives a linear response over the pCa range 1–5 with a slope of 27.4 mV (pCa)^–1. The sensor can be used for the pH range 3–8.5. The calcium-selective membranes were characterized in terms of their surface morphology and the structural parameter, the glass transition temperature. The ac impedance and FTIR analysis of the polyimide-based polymeric membrane were also studied.