This work, the etching characteristics of Ba2Ti9O20(BTO) thin films were investigated using an inductively coupled plasma (ICP) of Ar/Cl2 gas mixture. The etch rate of BTO thin films as well as the BTO/SiO2 and BTO/PR etch selectivity were measured as functions of Ar/Cl2 mixing ratio (0∼100% Ar) at a constants gas pressure (6 mTorr), total gas flow rate (50 sccm), input power (700 W) and bias power (200 W). The etch rate of BTO thin films decreased with increasing Ar fraction. To analyze the etching mechanism an optical emission spectroscopy (OES), double Langmuir probe(DLP) and surface analysis using X-ray photoelectron spectroscopy (XPS) were carried out.