A set of Cr1−xCux alloy films with 0<x<1 and Cr∕Cu multilayered films (MLFs) has been prepared by dc sputtering onto glass substrates kept at 293K. The x-ray diffraction study reveals the formation of continuous solid solutions in bcc structures for the Cr1−xCux alloy films with x<0.3 and in fcc structures for x>0.3. The structural instability of Cr1−xCux alloy films near x≈0.3 is discussed in terms of band structures of Cr–Cu alloys with bcc and fcc types of structure, and related to the dramatic changes of the density of states at the Fermi level. The optical properties of Cr1−xCux alloy films can be classified into two groups, representing the film structures. The fcc-bcc structural transformation results in the appearance of interband absorption at 2eV in the optical-conductivity spectra of alloy films, which originates from Cr. The observed changes in the experimental optical properties of Cr1−xCux alloy films are explained in terms of band structures of Cr–Cu alloys. The comparison between experimental and modeled optical properties of Cr∕Cu MLF enables us to conclude that the interfacial alloy regions of about 1.6–2.2nm in thickness are spontaneously formed during the Cr∕Cu MLF fabrication. In addition, it was understood that the main features of electronic band structures for pure Cr and Cu sublayers of a few nanometers in Cr∕Cu MLF resemble greatly those of the bulk Cr and Cu.