This study examined the resistance switching mechanism of the W tip/40 nm NiO/Ir and Pt/40 nm NiO/Ir structures in a voltage sweep mode. The results showed that the conducting filaments propagate from the anode interface, and resistance switching is induced by the rupture and recovery of the conducting filaments in the localized regions near the cathode. This is in contrast to what is observed in TiO2 [Kim et al., Appl. Phys. Lett., 91, 012907 (2007)], where the filamentary switching occurs at the anode interface. NiO is a p-type electrical conduction material. Localized hole injection at the anode interface induced the removal of oxygen ions from NiO to the anode (or atmosphere) by the Joule heating-assisted electromigration. This eventually leads to the metallic Ni filament formation extending from the anode interface to the cathode interface. The weaker Ni filament near the cathode interface induced a larger local heat generation for the given switching currents, which leads to the cathode interface localized switching. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3240201] All rights reserved.