This paper deals with changes in the internal friction at room temperature of Hadfield steel by annealing. The transversal resonant vibrattion was established by the electro-magnetic method. Then, its internal friction was obtained from the free decay of resonant vibration after the driving electric current was switched off. Experimental results obtained are as follows:(1) A specimen annealed after solution treatment or as-solution treated was found to have strain amplitude dependent in hardness.