The electrochromic properties of mixed Nb/Fe-oxide films with amorphous structure which were prepared via the sol-gel route were determined. Films with Nb/Fe molar concentration ratios 0.2:1, 0.4:1, and 1:1 exhibit ion-storage capacities up to 18 mC/cm(2) depending on Nb/Fe molar ratio. Electrochromically films behave as optically passive electrodes with a coloration efficiency of nearly zero at lambda > 480 nm, while at, shorter wavelengths a relatively strong anodic coloring was observed, yielding negative coloration efficiencies up to -20 cm(2)/C. Coloring/bleaching changes of films are correlated with the ex situ IR spectroscopic measurements of charged/discharged films showing distortions of the film structure with Li+ ion insertion/extraction reactions. Electrochemical stability of Nb/Fe (0.4:1)-oxide films was tested up to 2000 cycles in a sol-gel electrochromic device consisting of sol-gel-derived WO3 films and hybrid organic/inorganic ionic conductor with ionic conductivity of about 10(-4)S/cm serving for lamination of the electrodes.