The electric conduction of iodine-doped poly(3-octylthiophene) thin films has been evaluated by independently driven double-tip scanning tunneling microscopy. We investigated the lapsed time dependence of the conduction of the film between the two tips for various amounts of iodine doping. The variation of the conduction between the two tips indicated that both the thermal diffusion and direct-current voltage-induced diffusion of the iodine atoms occurred in the thin films. (c) 2005 Elsevier B.V. All rights reserved.