The machinability of high-temperature aluminized steel, wherein hot-dip aluminum-coated steel is heated to 1000 β’ C, was investigated by machining the material using a cemented carbide tool. It was confirmed that the alloy layer formed by the high-temperature aluminizing consisted of an Fe 2 Al 5 layer, an FeAl layer and an aluminum solid solution (β£Fe(Al)). With increasing diffusion time, the thickness of the FeAl layer and the β£Fe(Al) layer increased while the thickness of the Fe 2 Al 5 layer decreased. During the machining of the aluminized steel at a cutting speed of 1.5 m/s, the tool temperature rose rapidly, in particular during cutting of the FeAl layer. Flank wear during cutting of the Fe 2 Al 5 layer was not greatly affected by changing the cutting speed. In contrast, flank wear during cutting of FeAl was smaller at a lower cutting speed. The machined surface roughness was larger for cutting of the Fe 2 Al 5 layer and the FeAl layer region because of brittle fracture on the machined surface, whereas it decreased with increasing distance from the surface to a minimum at the β£Fe(Al) layer region.