Upilex-s [poly(biphenyl dianhydride-p-phenylene diamine)] polyimide have been widely employed in the area of flexible electronics. For its potential application on fabricating flexible solar cells, the optical properties of Upilex-s are measured in this paper. Intrinsic hydrogenated amorphous silicon layers are then deposited on Upilex-s substrates at temperatures 100°C and 180°C by plasma enhanced chemical vapor deposition (PECVD) system. As an comparison, intrinsic a-Si:H layers are also fabricated on glass substrate of Corning2000. Both layers on flexible and rigid substrates are thoroughly characterized by activation energy and dark conductivity measurements. It can be concluded that the intrinsic layer on Upilex-s has favorable properties and could be a competitive candidate as substrate materials of flexible solar cells.