Macrocyclic hexaoxazole dimer of L2H2-6OTD-dimer (3) was newly synthesized as a telomeric G-quadruplex (G4) ligand, and interaction with long telomeric DNAs telo48, 72, and 96 was evaluated by means of electrophoresis mobility shift assay, CD spectra analysis, and CD melting experiments. The L2H2-6OTD-dimer (3) interacted with the long telomeric DNAs by inducing anti-parallel type G4 structure of each unit of 24 bases, i.e., (TTAGGG)₄ sequences. Dimer 3 stabilizes long telomeric DNAs more efficiently than the corresponding monomer of L2H2-6OTD (2). It showed potent inhibitory activity against telomerase, with an IC₅₀ value of 7.5 nm.