Abstract
Electrically conducting composite films have been prepared from the polymer solution of conducting poly o‐phenylenediamine (PoPD) and nonconducting polyvinyl alcohol (PVA). This composite film showed a very low value of the percolation threshold (0.1 volume percent of the PoPD content) where the conductivity rose sharply. On the other hand, the conductivity of the prepared composite film was linearly related to the atmospheric humidity, extending from 
. The humidity‐dependence of the conductivity was caused by the change in the acid‐base equilibrium between the PoPD and PVA in the composite film.