Ferroelectric YMnO thin films were etched with Ar/C1 and CF/C1 Plasma. The maximum etch rate of YMnO thin film was 300 /min at a Cl/Ar gas mixing ratio of 8/2, an RF power of 800 W, a do bias of-200 V, a chamber pressure of 15 mTorr, and a substrate temperature of 3. From the X-ray photoelectron spectroscopy (XPS) analysis, yttrium was not only etched by chemical reactions with Cl atoms, but also assisted by Ar ion bombardments in Ar/C1 plasma. In CF/C1 plasma, yttrium formed nonvolatile YF compounds and remained on and the etched surface of YMnO. Manganese etched effectively by forming volatile MnCl and MnF. From the X-ray diffraction (XRD) analysis, the (0004) diffraction peak intensity of the YMnO thin film etched in Ar/Cl plasma shows lower than that in CF/Cl plasma. It indicates that the crystallinty of the YMnO thin film is more easily damaged by the Af ion bombardment than the changes of stoichiometry due to nonvolatile etch by-products.cts.s.