Hybrid metal nickel/cobalt hexacyanoferrate (Ni/CoHCNFe) has been prepared in the form of thin films on electrode surfaces and as bulk precipitates (powders). This heteronuclear metal hexacyanoferrate cannot be considered a simple mixture of hexacyano-ferrates of nickel and cobalt, and it shows different voltammetric and electrochromic characteristics in comparison to the respective single-metal hexacyanoferrates. On the basis of X-ray absorption, elemental analysis, and comparative voltammetric measurements, the following approximate formulas, (K2Ni0.5Co0.5II)-Co-II[Fe-II(CN)](6) and (KNi0.5Co0.5II)-Co-II[Fe-III(CN)(6)], have been proposed for the predominant reduced and oxidized forms of hybrid Ni/CoHCNFe. The results are consistent with the existence of linear units -Fe-CN-Co-NC-Fe-CN-Ni- in the structure. Hybrid nickel/cobalt hexacyanoferrate film has unique electrochromic properties, and it shows long-term stability and promising charge storage/transport capabilities during voltammetric potential cycling.