Paneth cells are cells in the small intestine epithelium, alongside goblet cells, enterocytes, and enteroendocrine cells. Some can also be found in the cecum and appendix. They are below the intestinal stem cells in the intestinal glands (also called crypts of Lieberkühn) and the large eosinophilic refractile granules that occupy most of their cytoplasm.

These granules consist of several anti-microbial compounds and other compounds that are known to be important in immunity and host-defense. When exposed to bacteria or bacterial antigens, Paneth cells secrete some of these compounds into the lumen of the intestinal gland, thereby contributing to maintenance of the gastrointestinal barrier by controlling the enteric bacteria. Therefore, Paneth cells play a role in the innate immune system.

Paneth cells are named after 19th-century pathologist Joseph Paneth.