Cyclic voltammograms of pyrrole monomer and polypyrrole films prepared potentiostatically at 1.0 V versus an Ag/AgCl electrode have been examined. The insulating natural fibers, such as cotton, silk, and wool become electrically conducting when they are subjected to electrical treatment in the polymerizing solution of pyrrole in acetonitrile containing p-toluenesulfonic acid as a supporting electrolyte. The weight gain and the electrical conductivity of the fibers increase with the time of electrolysis and impressed current levels. The conductivities are in the range of 0.2 to 15 s/cm and dependent on the nature of the fibers.