Abstract: The electrochemical and optical properties of a smart window consisting of two complementary elecrtochromic materials, namely polyaniline and tungsten oxide, have been investigated. The kind of smart window depcts remarkable properties for light modulation in the visible region. By Changing the applied voltage from-1.4V to +1.4V, for example, the transmission is reduced from 0.770 to 0.178 at 550nm, and from 0.680 tO 0.085 at 720nm. A smart window consisthe of Polyanilinetitaniumdioxide composite film and tungsten oxide filn has also ho investigated. It deminstrates sharp light modulation in the visible region, and as a result of the addition ofTiO2, the requesite variation in applied potential for the equivalent amount amount of electro chromic reduced. For exzmple, by changing the applied voltage from-1.4V to + 1.0V,the transmission is changed from 0.745 to 0.048 at 720nm.