A dimeric form of 2-amino-1,8-naphthyridine derivative ND binds to human telomeric sequence d(TTAGGG)n by strong stabilization of G-G mismatches in the hypothetical duplex of the sequence, and inhibits the elongation of the sequence by telomerase. To gain higher affinity to the telomeric sequence, we have synthesized naphthyridine tetramer NT which contains four naphthyridine chromophores. Tm measurements of the telomeric sequence in the presence of NT and ND indicated that NT binds more strongly to the telomeric sequence than ND. Electrospray ionization mass spectorometry of the complex between NT and 15-mer telomeric sequence clearly showed that one molecule of NT bound to the 15-mer sequence. This suggested that the 15-mer forms hairpin-like structure in the complex, and the resultant of the G-G mismatches were stabilized by NT.