The heterometallic Cu–In complex salt [Cu(III) (dtc)2][In(III)I4](1) (dtc = S2CNEt2, diethyldithiocarbamate) was prepared by reactions of Cu(II) (dtc)2 and In(III)I3 in benzene solution. As a redox reaction, Cu(II) (dtc)2 was oxidized to [Cu(III) (dtc)2]+, and In(III)I3 was changed to [In(III)I4]−. The square−planar Cu(III)S4 local symmetry of 1 involves a distorted octahedral coordination environment via long−range intermolecular interactions and represents a new one-dimensional structure of [Cu(III) (dtc)2]+ units. The crystal packing system of 1 consists of many [Cu(III) (dtc)2]+ chains surrounded by six parallel chains without solvent molecules. The infrared spectra of 1 showed a higher-frequency C–N thioureide bond in Cu(III) (dtc)2 than that of pristine Cu(II) (dtc)2, which has a lower oxidation state due to the Cu(II) center.