This work was conducted to study the histological properties and distribution of mucous cells in digestive tract by conventional paraffin section, H.E and AB-PAS (Alician blue and periodic acid Schiff reagent, Alician blue at pH 2.5) staining in Carcinoscorpius rotundicauda. The digestive tract shaped as a tube with branch structure in the zone of midgut (Fig. 1). H.E staining showed that esophagus, stomach, pyloric stomach, midgut and hindgut of this species showed general structure of digestive tract. From inner to outer of the digestive tube were mucosa, submucosa, muscularis, and serosa layer. A short and tubular esophagus was featured by thin muscularis but thick deeply chitin layer (Fig. 2a, b); Stomach was expanded with thick longitudinal folds and chitin layer coating in the mucosa surface (Fig. 2c, d, e). There pyloric stomachs trapped into midgut with both thin but recognizable muscularis and chitin layer (Fig. 2f, g); there was no remarkable difference in structure between midgut and hindgut, they both had numbers of mucosa fold and mucous cells locating in epithelium, but there was no chitin layer (Fig. 2h﹣l). Results of AB-PAS staining showed that there existed typeⅠ and typeⅡ mucous cells in digestive tract and their distribution characteristics were different in number and shape through the digestive tract. No mucous cell was detected in esophagus and pyloric stomach, but typeⅡ mucous cells were found in submucosa layer of stomach (Fig. 3a). Mucous cells distributed in mudgut and hindgut were superior in quantity than in stomach to some extent, especially in gut zone near pyloric stomach. The majority of mucous cells was TypeⅡ in midgut, mainly distributed in submucosa layer and mucosa epithelium (Fig. 3b, c). TypeⅠ mucous cells were found in submucosa layer and numerous typeⅡ mucous cells were found in mucosa epithelium of hindgut (Fig. 3d﹣f). The histological characteristics of digestive tract of C. roundicauda reveal that the functions may differ in different parts of digestive tract, and it may indicate a coordination between feeding habit and digestive tract structural evolution in C. rotundicauda.