The types and distribution of mucous cells in the alimentary canal of Cheilinus undulates Rüppell were studied using the AB-PAS (Alcian blue and periodic acid Schiff's reagent) staining method. The mucous cells are distributed in every part of the alimentary canal of Cheilinus undulates Rüppell, however, the cell densities and cell types vary at different locations. Type Ⅱ mucous cells are mainly located near the gastrovascular cavity, while type Ⅲ and type Ⅳ mucous cells are mainly found in the bottom of the mucous layer. Buccopharyngeal cavity, tongue and esophagus mainly posesse type Ⅱ and type Ⅳ mucous cells. The top of protuberances in small intestine and recta is characterized by type Ⅱ and type Ⅳ mucous cells, and the bottom is characterized by type Ⅲ and type Ⅳ mucous cells.KEY WORDSCheilinus undulates RüppellDigestive tractMucous cellsTypes and distribution