The preparation process of a molecularly imprinted overoxidized-polypyrrole film has been studied with the quartz crystal microbalance. The film has been derived from 1-naphthalenesulfonate (1-NS)-doped polypyrrole through overoxidation. The extraction of 1-NS (dedoping) has created a shape-complementary cavity at the surface. The resulting overoxidized-polypyrrole film imprinted with 1-NS exhibited an excellent selectivity to the structural isomer, 1-NS. Aqueous 0.010 M 1-NS showed a frequency decrease of 110 Hz, while 2-NS shows only a negligible change. Thus, the shape-complementary cavity can recognize the difference in the spatial configuration of the SO3- substituent between the 1 and 2 positions. (C) 2002 The Electrochemical Society.