The size effect, the length dependence of actuation behavior, of anisotropic polypyrrole (PPy) film obtained by electrochemical polymerization in a thin slab vessel consisting of PTFE walls has been studied. It was found that the active area of the actuator is limited within 3 mm from the electrolyte surface when it is simply soaked in the electrolyte. The active area is doubled by electrically insulating the actuator from the electrolyte surface. These results suggest that the active area of the PPy actuator is mainly limited by two factors, the enhancement of electrochemical reaction rate at the electrolyte surface and the reduction of electrical conductivity of the actuator upon undoping.