AbstractWe have investigated a method of preparing a large‐size anisotropic polypyrrole (PPy) film using a slab vessel consisting of poly(tetrafluoroethylene) (PTFE) walls as well as its actuation abilities. The PPy film can be grown along one side of the PTFE walls and exhibits morphological anisotropy of the PPy packing density along the thickness direction. A piece bends in a regular direction (the surface in contact with the PTFE wall) and reverts during a redox cycle without the use of any additional processes such as lamination. The actuation properties of the anisotropic PPy actuator strongly depend on the size of the cation in the driving electrolyte, and the bending behavior of this actuator at room temperature becomes slower for larger cations. On investigating the temperature dependence of actuation properties, the arrival time of the actuator (the time required for the tip of the actuator to touch the electrolyte surface upon stepwise potential change) was found to become shorter in all electrolyte solutions with different electrolytes. This result can be understood in terms of the thermally activated microscopic movement of the PPy main chains. Such behavior based on electrochemical stimulus not only provides information related to ionic transfer and storage but also suggests that the anisotropic PPy film can be put to practical use as an electrochemical actuator for artificial muscle which directly converts electrical energy into mechanical energy. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(4): 7–13, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20066