SrBi2Ta2O9 (SBT) thin films were etched with a varying CF4/Ar gas mixing ratio in a magnetically enhanced inductively coupled plasma system while a r.f. power, a d.c. bias voltage, and a chamber pressure were fixed. When the samples were etched at a r.f. power of 600 W, a d.c.-bias voltage of - 300 V, a chamber pressure of 10 mtorr and a CF4(10)/Ar(90) gas mixing ratio, the etch rare of SET thin film was 1650 Angstrom /min and the selectivity of SET thin film to photoresist and SiO2 were 0.89 and 0.6, respectively. The chemical reactions on the etched surface were examined with X-ray photoelectron spectroscopy and secondary ion mass spectrometry. From these results, it can be concluded: Sr interacted with the F radical, but remained at the surface due to nonvolatility of SrFx; Bi was removed by Ar ion-bombardment rather than by chemical interaction with the F radical and Ta was etched by interacting with the F radical with the help of Ar ion-bombardment to break a Sr-Ta-O bond.