Impedance spectroscopy was applied to MnOx-based thin films prepared in symmetric and asymmetric electrode configurations, i.e., Pt/MnOx/Pt and Ta/MnOx/Pt, respectively. Equivalent circuit analysis suggests the presence of higher resistance surface layers adjacent the electrodes, in addition to a higher conductivity component at central portions of the MnOx thin films. The asymmetric configuration enables the Ta/MnOx interfacial layer to facilitate the redox transport of oxygen ions, where significant changes in resistance with the electric field are responsible for the higher on/off resistance ratio in Ta/MnOx/Pt. The higher dielectric constant and bias-dependent capacitance and resistance support the coexistence of both oxidized surfaces and interfacial layers.