Herein, we report for the first time the application of a sumanene derivative in potentiometric recognition of caesium cations. The structure of the sumanene receptor was carefully tuned to obtain its compatibility with polyvinyl chloride plasticized membranes of potentiometric sensors. The developed ion-selective electrodes based on membranes doped with octyloxybenzene sumanene exhibited a near theoretical sensitivity towards caesium cations, with a detection limit of 4 μM Cs+.