Wear maps ofa SiaN 4 ceramic cutting tool for cutting 1045 plain carbon and 302 stainless steels are produced in this paper. Through the systematic turning tests, the optimum cutting regions were determined on the wear maps of a two-dimensional diagram of cutting speed and feed rate. They are important for selecting the appropriate cutting parameters for a ceramic tool when cutting different workpieces. The wear morphologies and wear mechanisms for the different regions were investigated by scanning electron microscopy (SEM) with energy dispersive analysis of x-ray (EDX), and the corresponding cutting temperature distributions were measured by a thermal video system. Based on the experiment results, the relationships between cutting conditions, cutting temperatures, and wear mechanisms were discussed in detail.