Compared to the commercial ceramic tool SG4, the performances of nano scale ZrO2 toughening Al2O3 matrix ceramics tool in machining the hardened 40Cr alloy steel, such as A15Zc and A20Z(c+m),were studied. When the hardened 40Cr alloy steel is machined, the tool flank wear widthes of A15Zc and A20Z(c+m) are increased with an increase of the cut depth and the effect of cutting speed on cutting performance is small. A15Zc and A20Z(c+m) have stronger wear resistance than SG4 at the smaller cut depth. The main wear patterns are tool wear on the rake face and flank, and the main wear mechanisms are bonding wear on tool rake face and abrasive wear on tool flank.