Ionic liquids (ILs) are successfully implemented in various fi elds of science including improvement of analytical characteristics of ion-selective sensors based on polymeric plasticized matrices. However, utilization of ILs in optical sensors has not been studied extensively thus far. In this contribution, we demonstrate how gradual replacement of the conventional plasticizer by an ionic liquid affects optical response characteristics. The shift of the sensor dynamic range originating from the ion exchange constant decrease upon adding the IL was observed. The possibility of developing IL-based optical sensors of individual ionic activity was demonstrated as well.