High temperature Zircaloy-4 oxidation has been studied through two-stage oxidation experiments using 18O isotope. 18O distribution in the oxidation scales was investigated by micro-Raman imaging. First, zirconia standards with known 18O content were prepared and analyzed for calibration purposes. Then, to assess the method on a simple case, 18O tracer penetration patterns were recorded after a 800°C two-stage oxidation. Finally, oxidation at 850°C of a Zircaloy4 cladding tube pre-corroded at 425°C to simulate corrosion during normal reactor operation was studied. These preliminary results give insights on the protective nature of the first formed zirconia scale in case of an accident. © 2015 Elsevier Ltd.