In-situ deposition of conducting polypyrrole thin films on an insulating substrate has been achieved by chemical polymerization of pyrrole on a modified surface. The surface modification agent was a silane compound bearing a pyrrole group; C ₄ H ₄ NC ₃ H ₆ Si(OMe) ₃ which attached to the SiO ₂ -Si surface via molecular self-assembly. A monolayer of silane-bearing pyrrole molecules was formed on the surface. Polymer films formed on the silane-modified surfaces showed better adhesion compared to those on the unmodified surfaces. IR, UV–VIS–NIR and XPS data revealed that the films were in their conducting state and homogeneously doped. The thickness and conductivity of the resulting films were controlled by the preparation conditions, such as choice of solvent, deposition time and pyrrole to oxidant ratio. Polypyrrole films with thickness in the range 410–5500 Å adhered firmly on the surface. The room-temperature conductivity of the films can be up to 1.6 S cm ^-1 . Some of the polypyrrole films showed anisotropic conductivity which indicates that the pyrrole molecules on the surface induced regular deposition of polypyrrole chains on the substrate.