In this paper, the effects of UV irradiation on the optical and electrical properties of poly(di-methyl silane) thin films prepared by the vacuum evaporation technique have been examined by measuring the direct and alternating currents as well as the optical absorption spectra. As a result, it is found that the electric conductivity increases with increasing irradiation time. It is also found from the alternating current measurement that both the real and the imaginary parts of the complex dielectric constant increase with increasing irradiation time. From the optical absorption spectra, the origin of these results is attributed to a decrease of the chain length of the poly(di-methyl sitane) molecules, and an increase of the number of Si -O bonds by UV irradiation. (c) 2005 Elsevier B.V. All rights reserved.