Scanning tunneling microscopic images of doped polyaniline (PANI) with HCl are presented. Parallel chains with average separation of 0.4 nm are clearly visible, and the measured distance between the nearest two maxima in the polymer chain is about 1.04 nm. Molecular-mechanic calculations were used to optimize the conformation of a model polyaniline chain, and have yielded numerical values which agree well with measurements taken from the STM images.