This paper focuses on the influence of difference of tool materials on generation of wear protective layer when turning gray cast iron containing Al and Mg. In this experiment, the gray cast iron to which small quantities of Al and Mg was added were cut with cermet, P grade carbide (P10), silicon nitride ceramics (Si3N4), titanium nitride (TiN) coated carbide and K grade carbide (K10) at high speed. In turning gray cast iron containing Al and Mg with cermet, the tool wear was significantly reduced compared to that resulting from the cutting of conventional gray cast iron. Further, the protective layer consisting of nonmetallic inclusions in the work material was formed on the tool surface. In addition to cermet, this layer was formed on tool surface of Si3N4 and TiN coated carbide. The elements of Al and Mg added to the work materials were detected in the layers formed on these tool surfaces as well as cermet. The inhibiting effect on tool wear was also caused when turning with P10. However, P10 had much greater wear than cermet. On the other hand, in the case of turning with K10, the effect reducing wear with the addition of Al and Mg was not caused. The wear increased as cutting speed increased regardless of work materials.