Natural fibres constitute interesting, low cost and environmentally friendly precursors of carbon fibres. However, they are prone to fuse and degrade upon thermal treatment, affecting the properties of the products unless a stabilization step was included. Aiming to reach a better understanding of the stabilization mechanism of wool as a potential precursor for the preparation of carbon fibres, in this study we have analysed the chemical, structural and morphological transformations during its oxidative stabilization in air. Below 400 °C, both the structure and morphology of the fibres were preserved. The chemical composition changed with the stabilization temperature; main changes include the loss of secondary protein structure, cleavage of sulphur bridges, dehydration, oxidative crosslinking and rearrangements of N-groups through the formation of carbodiimides. Oxidation of the wool at 300 °C rendered materials with a fibrous morphology and high carbon yield (ca. 36 wt%), yielding carbon fibres upon carbonization at high temperatures.