The effect of storage time without use (STWU) in the supporting electrolyte solution on the conducting properties of poly(o-aminophenol) (POAP) film electrodes was studied. Cyclic voltammetry (CV), rotating disc electrode voltammetry (RDEV), electrochemical impedance spectroscopy (EIS) and surface resistance (SR) were employed. The storage of a POAP film without use for time periods longer than 32 h strongly reduces its electroactivity. Here, this effect is called deactivation. The attenuation of the voltammetric response of the polymer film with the increase of the storage time allows one to define a degree of deactivation (θ_d). A decrease of the electron transport rate (D_e) with the increase of the degree of deactivation of POAP films was obtained from RDEV measurements. The relative surface resistance change (ΔR/R) of a gold film coated with POAP is also attenuated by the increase of the STWU. Impedance spectra of deactivated and nondeactivated POAP films in the presence of an electroactive solution and in the sole presence of the supporting electrolyte were analyzed on the basis of two different impedance models. As the deactivation of POAP films by the STWU studied in this work was compared with deactivations caused by other electrochemical and chemical treatments, such as prolonged potential cycling (PPC), high positive potential limits (HPPL) and soaking in a ferric ion solution (SFeIS), this paper can be considered as a review, where the most significant studies that have been reported about the stability of POAP are documented.