As a polyaniline film was irradiated by a laser with 668 nm in acidic solution, the light was dispersed by Rayleigh scattering when a negative potential was applied to the film. From the angular dependence of the scattering light intensity which was detected with a photo-diode on an x-y stage, clusters 4 to 5 mu m in average diameter were detected. The size was estimated by applying the theory of interference of the fight scattering at large particles. A pattern like an assembly of bubbles was found through an optical microscope only at negative potentials. It was also found when the chemically reduced film was exposed to air. When 1-methyl-2-pyrrolidone, a solvent of polyaniline, was mixed with water as a solvent in the electrochemical scattering experiment, the intensity decreased with an increase in the molar ratio of 1-methyl-2-pyrrolidone, being more than the loss of the firm by dissolution. The size of the clusters increased linearly with the logarithm of the electrochemical reduction time. This is the slow relaxation or the memory effect of conducting polymers. The cluster was thought to be an aggregation of the conducting species.