Tantalum oxide and tungsten oxide thin films were prepared by spin coating techniques. The effect of tantalum concentration on the optical, structural and electrochromic properties of the films were studied. The optical, structural and electrochromic properties of pure, WO3, Ta2O5 and Ta2O5 doped WO3 thin films are described and compared to each other. Film characterization was made by cyclic voltammetry (CV) and scanning electron microscopy (SEM). The coatings were studied electrochemically in I M LiClO4 in propylene carbonate electrolytes. Electrochemical and optical characterizations show that the tantalum concentration affects the properties of sol-gel derived films significantly. Mechanical tests show that tantalum oxide films resist to abrasion well.