The coordinative properties of perfluoro-15-crown-5 with monocations were investigated using 19F NMR spectroscopy and ion-selective electrodes with perfluoro-15-crown-5 as the matrix of their sensor membranes and the fluorophilic tetrakis[3,5-bis(perfluorohexyl)phenyl]borate as ion exchanger site. The results show that perfluoro-15-crown-5 interacts weakly but significantly with Na+ and K+. Assuming 1:1 stoichiometry, the formal complexation constants were determined to be 5.5 and 1.7 M−1, respectively. This weak binding is consistent with the strong electron withdrawing nature of the many fluorine atoms in the perfluorocrown ether. While perfluorinated crown ethers have been known to form host–guest complexes with the anions O2− and F− in the gas phase, this is the first study that quantitatively confirms cation binding to a perfluorocrown ether.