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A ceramic knife is a knife made out of very hard and tough ceramic, often zirconium dioxide (ZrO2; Also known as zirconia). These knives are usually produced by dry pressing zirconia powder and firing them through solid-state sintering. The resultant blade is sharpened by grinding the edges with a diamond-dust-coated grinding wheel. Zirconia ranks 8.5 on the Mohs scale of mineral hardness, compared to 6 to 6.5 for hardened steel, and 10 for diamond. This very hard edge rarely needs sharpening.

Zirconium oxide is used due to its polymorphism. It exists in three phases: Monoclinic, tetragonal, and cubic. Cooling to the monoclinic phase after sintering causes a large volume change, which often causes stress fractures in pure zirconia. Additives such as magnesium, calcium and yttrium are utilized in the manufacture of the knife material to stabilize the high-temperature phases and minimize this volume change. The highest strength and toughness is produced by the addition of 3 mol% yttrium oxide yielding partially stabilized zirconia. This material consists of a mixture of tetragonal and cubic phases with a bending strength of nearly 1200 MPa. Small cracks allow phase transformations to occur, which essentially close the cracks and prevent catastrophic failure, resulting in a relatively tough ceramic material, sometimes known as TTZ (transformation toughened zirconia).

Ceramic knives will not corrode in harsh environments, making them popular with scuba divers. They are also nonmagnetic and do not conduct electricity, which can be useful during bomb disposal operations. Their chemical inertness to extreme pHs, and their ability to retain a cutting edge longer than forged metal knives make them a suitable culinary tool for slicing boneless meat, vegetables and fruit. Since they are brittle they may break if dropped on a hard surface, and cannot be used for chopping through bones or frozen foods, or in other applications which require prying, which may result in chipping or catastrophic failure. Several brands now offer a black colored blade made through an additional hot isostatic pressing (HIP) step, which improves the toughness.

Ceramic knives may present a security problem as ceramics are not seen by conventional metal detectors. To hinder misuse of concealed knives many manufacturers include some metal to ensure that they are seen by standard equipment. Ceramic knives can be detected by extremely high frequency