Monoclinic alpha- NaMnO2 is re-investigated electrochemically as a positive electrode material for sodium ion batteries. About 0.85 Na can be deintercalated from NaMnO2 and 0.8 Na be intercalated back during potentiostatical intermittent charge and discharge. Galvanostatical cycling between 2.0 V and 3.8 V gives 185 mAh/g discharge capacity for the first cycle at C/10 rate and 132 mAh/g remains after 20 cycles. Charge and discharge curves are significantly different indicating more hysteresis than is typical for lithium intercalation compounds. We also explain the remarkable difference between layered LiMnO2 and NaMnO2 upon alkali removal. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.035112jes] All rights reserved.