Hardness of oxide scales on Fe-(0, 0.5, 1.5, 3.0)Si alloys was studied at room temperature after oxidation at 1273 K for 18 ks in oxygen, and at 1073 and 1273 K for 180 and 1080 ks in dry air, by micro-Vickers hardness measurements. After oxidation at 1273 K for 18 ks, high-temperature hardness of oxide scales on Fe-(0, 1.5, 3.0)Si alloys was also measured at 1273 K Oxide scales on Fe-Si alloys were mainly Fe(2)O(3), Fe(3)O(4), FeO and Fe(2)SiO(4). Hardness of Fe(2)O(3), Fe(3)O(4) and FeO on Fe was 6.7, 4.0 and 3.5 (GPa), respectively, and hardness of Fe(2)O(3) on Fe-Si alloys slightly increased with increasing silicon content at room temperature. At 1273 K, hardness of Fe(3)O(4) and FeO on Fe was 0.08 and 0.05 (GPa), respectively, and hardness of Fe(2)O(3) on Fe-1.5Si alloy was 0.32 (GPa), and that of Fe(2)O(3) and Fe(2)SiO(4) on Fe-3.0Si alloy was 0.53 and 0.63 (GPa), respectively.