Abstract The oxidation of phenol using mill scale (waste material produced during the hot rolling of steel) as iron source in a type Fenton process was investigated in this work. The mill scale was characterized by XRF, FT‐IR, XRD and SEM. The oxidation tests were carried at 25°C and atmospheric pressure, controlling the pH to 3.7. The phenol conversion and total organic carbon (TOC) removal as a function of catalyst loading (300–1000 mg/L) and phenol concentration (47 and 100 mg/L) were evaluated. The mill scale achieved high conversion of phenol (between 60.8 ± 2.2 and 94.5 ± 2.5%) and mineralization to CO 2 (between 38.9 ± 1.2 and 55.6 ± 2.5%) after 4‐h reaction. The mill scale showed a good catalytic performance, even after three cycles of reaction. Therefore, utilizing mill scale as a catalyst of the Fenton process is an alternative to the use of waste in the steel industry.