Polyaniline fibre microelectrodes prepared from a doped solution of polyaniline protonated with 2-acrylamido-2-methyl-1-propanesulphonic acid in dichloracetic acid were characterized electrochemically for the first time. Low scan rate cyclic voltammetry was used for characterisation in different acid electrolyte solutions, hydrochloric, nitric, perchloric, sulphuric and phosphoric, at low pH values with varying positive potential limits. Electrochemical impedance spectroscopy was also utilised. The electrochemical behaviour of polyaniline (PANI) fibres was found to be similar to that of PANI films obtained by electropolymerisation on metallic electrode substrates. The conduction potential window was found to be from +0.20 to +0.60V versus SCE, with small variations in the different acid solutions as well as with pH. The standard electrochemical redox couple hexacyanoferrate(III), was found to behave quasi-reversibly in the conduction potential region and rate constants were evaluated.