In the biological systems, there are various kinds of enzymes, containing metal ions such as iron(II), copper(II), zinc(II), manganese, etc. These enzymes are the catalysts for specific biochemical reactions, making the reactions to proceed under mild conditions. The metal ions are essential for the enzymes to form "reaction centers" for the catalytic reactions. In the field of nucleic acid chemistry, certain metal complexes have been known to have functions such as oxidative or hydrolytic DNA cleavage activities or inhibition of DNA or RNA polymerase activities. These functions are induced by intercalation of aromatic ligand moiety of the complexes, binding of the complexes to the minor or major groove of the double helical DNA, or covalent bond formation at N7 of neighboring guanines. Some DNA conjugates with rare earth metal complexes have been utilized as markers for detection of DNA base sequences due to their specific emission properties. In order to develop functional metal complexes that lead to anticancer reagents, artificial restriction enzymes, and DNA conjugates for detection of single nucleotide polymorphisms (SNP), we are studying following subjects.