Kasseri (Greek Κασέρι; from Turkish kaşer, kaşar) is a medium-hard pale yellow cheese made from unpasteurized sheep milk with very little, if any, goat's milk mixed in, in Turkey and Greece. It is a soft textured, stringy rather than crumbly, chewey, hard-rind cheese and belongs to the pasta filata family of cheeses, like provolone. The use of fresh unpasteurized milk is necessary to obtain the correct flavor and texture, and aging of at least four months is required for the development of flavor. In its aged stage it faintly resembles Parmesan or asiago but is not as creamy.

The name "Kasseri", produced in Greece is a protected designation of origin in the European Union.

Kasseri is consumed as is, in sandwiches or as main constituent in kasseropita pie.