Abstract: Al₂O₃-based ceramic cutting tool was used to turn 300M ultra high strength steel at high speed under dry cutting condition. Scanning electron microscopy (SEM) was employed to observe morphological features of worn surfaces produced by various wear mechanisms, and chemical composition in some worn areas of tool was analyzed by energy dispersive X-ray spectroscopy (EDS). Wear mechanisms in turning of ultra high strength steel by Al₂O₃-based ceramic cutting tool were studied. Results show that the major wear mechanisms of the ceramic cutting tool were adhesive wear, abrasive wear and oxidation wear. The dominant wear mechanism of rake face was adhesion wear that was affected by stress state on contact region between tool and chip. Oxidation wear appeared at the wear edge of rake face and flank face of ceramic cutting tool.