In situ scanning tunneling microscopy has been used to examine the structure of the aniline adlayer and the conformation of polyaniline molecules produced electrochemically on a Au(111) electrode in 0.1 M sulfuric acid containing 30 mM aniline. As evidenced by the high-resolution STM imaging, a simple method of potential step triggered electropolymerization of aniline molecules. This reaction propagated preferentially in the < 121 > directions to produce mostly linear polyaniline molecules. Molecular resolution STM yielded the internal structure of polyaniline molecules.