TiOx films were electrochemically deposited on TiN and Pt electrodes with a subsequent annealing under N-2 or O-2 ambient. The resistive switching characteristics of such TiOx films were investigated. The electrodeposited TiOx films showed bipolar resistive switching and the operation voltages such as electroforming voltage, and reset/set voltages showed a dependence on the annealing ambient, displaying higher operation voltages for the annealing under O-2 than for the annealing under N-2. The compositions of the different chemical states of species in TiOx films were observed to be modulated by the condition of electrochemical deposition and the subsequent annealing. The TiOx films annealed under the O-2 ambient showed a less concentration of nonlattice oxygen ions than under N-2 ambient. The reduction of nonlattice oxygen for annealing under O-2 was accompanied by the increase of Ti3+ in TiOx films and the increased reset/set voltages. It was concluded that the bipolar resistive switching of the electrochemically deposited TiOx film was strongly related to the nonlattice oxygen anions in the films. c 2010 The Electrochemical Society. [DOI: 10.1149/1.3516464] All rights reserved.