Highly Li+-selective ionophores based on 14- crown-4 derivatives were designed and synthesized, and the relationship of their molecular structures and ion selectivities was investigated in order to obtain a highly Li+-selective electrode. The ion selectivities were examined with 11 kinds of 14-crown-4 derivatives, which were prepared according to the proposed two types of Li+ ionophore models. Excellent Li+-selective ionophores were obtained by introducing a bulky “block” subunit into the ethano-bridge section of the base crown ring, which effectively prevents the formation of a 2:1 or 3:1 sandwich-type complex consisting of the crown ether and cations larger than Li+. The best Li+/Na+ selectivity (more than 1000) was obtained for the electrode using the 14- crown-4 derivative with a bulky decalin subunit. These results offer the general ion selectivity features of 14-crown-4-based compounds.