The mass transport of methanol mixed with ferric chloride hexahydrate (FeCl3. 6H(2)O) in poly(methyl methacrylate) (PMMA) and the related optical properties have been investigated. The ratio of FeCl3. 6H(2)O to methanol in the solvent mixture is X = 0.013, 0.038 and 0.063 g/g. The mass transport is anomalous, which is a mixture of Case I with Case II transport. Both diffusion coefficient for Case I and velocity for Case II transport satisfy the Arrhenius equation. The activation energy of diffusion coefficient in Case I transport decreases with increasing X, but the trend for that of velocity in Case II transport is opposite. The mass transport is an endothermic process and satisfies the van＇t Hoff＇s plot. The heat of mixing increases with X. The transmittances of PMMA saturated with the solvent and solvent of methanol mixed with FeCl3. 6H(2)O decrease with increasing X. The scattering intensity of the specimens after desorption is inversely proportional to the visible wavelength with an exponent, n, in the range from 1.02 to 3.25. The exponent is equal to 4 corresponding to the Rayleigh scattering. The wavelength dependence of scattering intensity is attributed to holes, the size of which is smaller than the visible wavelength, and to clouds. The holes and clouds in the solvent-treated specimen are observed by the scanning electron microscope and optical microscope. The deviation of the exponent n from 4 is due to the fractal dimension of hole and cloud. The FTIR spectra of specimens treated with solvent of different concentrations of FeCl3. 6H(2)O are also studied.