We find that resistance switching (RS) phenomena change reversibly between bipolar RS (BRS) and unipolar RS (URS) in a Pt/SrTiOx/Pt cell. For an asymmetric electrode configuration of Ti/SrTiOx/Pt cells whose top and bottom interfaces are Ohmic and Schottky-like rectifying, we determine that BRS only occurs when a positive voltage is applied to the bottom Pt electrode at the forming process. During the set process of BRS in a Pt/SrTiOx/Pt cell, O-2 bubbles develop on the top Pt electrode. From the experimental results for a single sample in which both BRS and URS occur, O2- ion movement and consequent interfacial resistance modification might play an important role in BRS but not URS. (C) 2012 Elsevier B.V. All rights reserved.