The electrical resistivity and the thermal expansion have been measured with iron-aluminium alloys containing from 9.75 to 11.66% aluminium, by treating them isothermally at the temperatures between 200°and 300℃ and also by cooling them to -183℃ from quenched state, K-state and Fe_3Al-ordered state. According to the results obtained, the alloys containing more than 10.65% aluminium, which show the characteristics of the K-state at first, transform into the Fe_3Al phase after passing through the K-state during the isothermal treatment. Further, the amount of the K-state in the alloys containing from 10.5 to 10.9% aluminium decreases at -183℃, and the alloys of more than 10.9% aluminium show the characteristics of the Fe_3Al phase at that temperature. Thus, it can be concluded that the K-state observed at room temperature is essentially of the Fe_3Al superstructure. However, the alloys containing less than 10.5% aluminium remain as the K-state even at -183℃. The difference in the nature between the alloys containing more and less than 10.5% aluminium remains to be clarified
