The etching characteristics of indium tin oxide (ITO) thin films in an O2/BCl3/Ar plasma were investigated. The etch rate of ITO thin films increased with increasing O2 content from 0 to 2 sccm in BCl3/Ar plasma, whereas that of ITO decreased with increasing O2 content from 2 sccm to 6 sccm in BCl3/Ar plasma. The maximum etch rate of 65.9 nm/m in for the ITO thin films was obtained at 2 sccm O2 addition. The etch conditions were the RF power of 500 W, the bias power of 200 W, the process pressure of 15 mTorr, and the substrate temperature of 40℃. The analysis of x-ray photo electron spectroscopy (XPS) was carried out to investigate the chemical reactions between the surfaces of ITO thin films and etch species.