The techniques of scanning tunneling microscopy and atomic force microscopy were used to study the structure of both chemically prepared free-standing and vacuum evaporated polyaniline thin films. Free-standing films were found to be largely amorphous, with small regions exhibiting semicrystallinity. No major structural differences between protonated and nonprotonated films were observed. Vacuum evaporated, nonprotonated polyaniline films consisted of a large-scale terraced structure composed of small, nanometer-scale polymer bundles. The average dimension of these bundles was 1000 angstrom. After protonation, the terraced structure was lost, with the surface becoming homogeneously flat.