This paper describes a new estimation method for the diffusion coefficient of acetophenone in insulating polymer using conduction current measurement. The conduction current of the sensor film, which was placed under the target film, was measured after the acetophenone was dropped on the upper side of target film. The diffusion coefficient estimated from the conduction current measurement shows good agreement with that from Fourier transform infrared spectrometer. It was concluded that the diffusion coefficient could be quantitatively assessed if the concentration of acetophenone, which brought the increasing conduction current, was known.