The atmospheric plasma (AP) surface treatment of a flexible indium zinc oxide (IZO) electrode grown on a poly(ethylene terephthalate) (PET) substrate was investigated as an alternative to oxygen vacuum plasma treatment for low cost organic solar cells. In this study, the surface properties of the flexible IZO electrode were modified by a simple AP treatment without changing their sheet resistance and optical transmittance. X-ray photoemission spectroscopy showed that the atmospheric air plasma treatment led to a decrease in the carbon content and an increase in the oxygen content at the surface of the flexible IZO electrode, indicating that the organic contamination on the flexible IZO electrode was effectively removed by the AP treatment. (C) 2009 The Electrochemical Society. [DOI:10.1149/1.3236387] All rights reserved.