Indium tin oxide (ITO) films coated on float glass slides were exposed to 5 eV hyperthermal atomic oxygen at room temperature with increasing fluences: 2×1019, 6×1019 and 2×1020 O-atoms/cm2. We characterized the structure of the ITO films after room temperature atomic oxygen exposure with scanning electron microscope (SEM) and atomic force microscope (AFM), synchrotron X-ray diffraction (XRD), and cross-sectional transmission electron microscope (X-TEM). The unexposed ITO films were found to possess a nano-crystalline surface, and clean and abrupt ITO/SiO2 interfaces without interfacial phase. Surface roughness of the exposed ITO films increased with the increasing AO influences. The interface- sensitive peaks in XRD measurements with grazing incidence revealed that the crystallinity of the ITO was modified near the interface. Cross-sectional TEM confirmed that many ITO particles with diameters ranging from 2-10 nm formed in the SiO2 substrate near the interface after AO exposure. These findings suggest that O atoms can travel through the ITO films, where the boundaries of columnar-grown grains may supply the pathway.