Developing novel methods for metal-induced switching of peptide structures expands the design principles of functional biomolecules and biomaterials. Here, a simple method for on-resin synthesis of dipicolylamine (Dpa)-containing peptides was developed. Whereas addition of divalent metal ions such as Fe(II) and Cu(II) to a peptide bearing a pair of Dpa moieties at the i and i + 4 positions led to the formation of a 1 : 1 complex of Dpa with metals, addition of Ni(II) yielded a cross-linked structure of Dpa-metal (2 : 1). This feature was utilized for the selective detection of Ni(II) using the peptide-Fe(II) complex. Repeated switching of the helical structure was also achieved by multiple additions of divalent metal ions to the peptide.