Single-stranded nucleic acids, which carry multiple negative charges in an aqueous medium at near neutral pH, are found to induce the aggregation and self-assembly of the positively charged alkynylplatinum(II) terpyridyl complexes via electrostatic binding of the platinum complexes to the single-stranded nucleic acids, as revealed by the appearance of new UV-vis absorption and emission bands upon addition of single-stranded nucleic acids to a buffer solution of the complex. Changes in the intensity and pattern of circular dichroism (CD) spectroscopy are also observed, many of which are consistent with the assembly of the platinum complexes into helical structures, via metal⋯metal and π⋯π stacking interactions. The induced spectroscopic property changes are found to depend on the structural properties of the nucleic acids.