The etching of Au thin films have been performed in an inductively coupled CF$_4$/Cl$_2$/Ar plasma. The etch rates were measured as CF$_4$ contents added from 0 to 30 % to Cl$_2$/Ar plasma, of which gas mixing ratio was fixed at 20%. Other parameters were fixed at an rf power of 700 W, a dc bias voltage of 150 V, a chamber pressure of 15 mTorr, and a substrate temperature of 3$0^{circ}C$. The highest etch rate of the Au thin film was 3700 $AA$m/min at a 10% additive CF$_4$ into Cl$_2$/Ar plasma. The surface reaction of the etched Au thin films was investigated using x-ray photoelectron spectroscopy (XPS) analysis. XPS analysis indicated that Au reacted with Cl and formed Au-Cl, which is hard to remove on the surface because of its high melting point. The etching products could be sputtered by Ar ion bombardment.