The machinabilities of aluminized steels were investigated by turning. The tool wear in cutting aluminized steels diffused at 1223K were more remarkably than steels as hot-dip aluminum coated, and the edge retreat amount increased with lengthening diffusion time TD. Three intermetallic compounds which were Fe_3Al, FeAl and Fe_2Al_5 formed to the diffusion layer of diffusion treated steels. In cutting frequency N was small, the machined surface roughness of diffusion treated steels were large because Fe_2Al_5 formed near the surface diffusion treated steels ware brittle fractured by impact while cutting. And, in N was large and Fe_3Al and FeAl were cut, the machined surface roughness were small. However, these intermetallic compounds caused temperature-rise and r remarkable tool wear.