The ion-selective electrode based on decalino-14-crown-4 was prepared and its Li+-selectivity against other alkali metal and alkaline earth metal ions was examined. The poly(vinyl chloride)-matrix membrane ion-selective electrode containing decalino-14-crown-4 as an ion selective ionophore and bis(butyl pentyl)adipate as a membrane solvent exhibited high Li+selectivity of at least 1000 times against all other alkali metal and alkaline earth metal ions. The ion selectivity factor (logkLi,Napot) for Li+/Na+was -3.3, which indicates that this electrode is one of the most selective for Li+/Na+. The electrode showed a linear Nernstian response slope ranging from 1 × 10−6to 1 M of Li+.