In this study homopolymer, copolymer, and composites of aniline and thiophene were synthesized in nitrogen atmosphere by using TEATFB (Tetraethyl ammonium tetrafluoroborate) and Lithium perchlorate as supporting electrolytes. In order to analyze their structure and characteristics, IR spectrums of the samples were taken and thermogravimetric analysis (TGA) was applied. Also, the samples were photographed under scanning electron microscope (SEM) for microstructure analysis and their electrochemical properties were observed and conductivities were obtained by four probe method. Homopolymerization and copolymerization reactions were carried out in two different solvents viz. acetonitrile and benzonitrile in order to see the solvent effect on polymerization. However, changing the solvent was found to have no significant effect on the resulting properties. It was concluded that changing the supporting electrolyte caused a structural difference in the resulting homopolymer. It also affects the properties considerably. During the bilayer preparation changing the coating turn led to variations in the properties of the samples. When polythiophene (PT) was coated with polyaniline (PA), the resulting system was a composite. However, in coating PA with PT the system was identified to be a copolymer. (C) 1996 John Wiley & Sons, Inc.