In this study, the optical activity of cellulose di and triacetate films with a highly oriented vitrified structure was studied. The systems possess high values of specific optical rotation [alpha], which is in favor of the formation of a cholesteric meso-phase. [alpha] depends on the sample orientation angle relative to the light polarization vector in the plane perpendicular to the light ray (optical activity anisotropy). This dependence (indicatrix) is irregular and is described by a distorted sinusoid in the Cartesian coordinates. The results of indicatrix decomposition into harmonic components are discussed, with the contributions of the isotropic and anisotropic components (each with the corresponding structural element of a certain symmetry type) being separated. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1605-1615,2009