The investigations of etch characteristics and mechanisms for indium tin oxide (In2O3)0.9:(SnO2)0.1 (ITO) thin films using HBr/Ar inductively coupled plasma were carried out. The ITO etch rate was measured in the range of 0%–100% Ar in the HBr/Ar mixture at fixed gas pressure (6 mTorr), input power (700 W), and bias power (200 W). Plasma parameters and composition were examined with a combination of plasma diagnostics by double Langmuir probe and global (zero-dimensional) plasma model. It was found that the ITO etch rate follows the behavior of Br atom flux but contradicts with that for H atoms and positive ions. This suggests that the ITO etch process is not limited by the ion-surface interaction kinetics and appears in the reaction-rate-limited etch regime with the Br atoms as the main chemically active species.