Polyaniline (PANI) micro/nanostructures are synthesized by electrochemical polymerization, and characterized by field-emission scanning electron microscopy, Fourier transform infrared spectroscopy and UV-visible spectroscopy. It is revealed that the PANI microwires are produced with high yield with diameters of about 2 μm and lengths of several hundreds of micrometers, while nanostructures in the presence of PAA have diameters of about 500 nm. The micro/nanostructured PANI films are very stable and show high electrocatalytic reduction toward H₂O₂, which makes it an ideal substrate for H₂O₂ detection and offers great promise for biosensing applications.