The type,distribution,size and secreting activity of mucous cells stained with H.E and AB-PAS(AB pH =2.6) in the epidermal tumor in Allogynogenetic Crucian Carp(Carassius auratus gibelio ♀ × Cyprinus carpio var.singuonensis ♂) have been studied under light microscope.Based on the observation after AB-PAS stain,the mucous cells in the epidermal tumor were divided into four types: Type Ⅰ which was only PAS positive was in red color,containing neutral mucoitin;Type Ⅱ which was only AB positive was in blue color, containing acid mucoitin;Type Ⅲ which was strong PAS positive and slight AB positive was in purple reddish color,containing mainly neutral mucoitin and slightly acid mucoitin: Type Ⅳ which was strong AB positive and slight PAS positive was in blue purple color,containing mainly acid mucoitin and slightly neutral mucoitin.The type Ⅰ and Ⅱ mucous cells were relatively fewer,and individually distributed among the epithelial cells of epidermal tumor.The secreting method of type Ⅰ and Ⅱ mucous cells was holocrine secretion.The type Ⅲ and Ⅳ mucous cell mainly distributed in cluster in the centre of leaf-like folds of tumor tissue.The secreting method of type Ⅲ and Ⅳ mucous cells was also holocrine secretion which gradually died and disappeared after secreting.When the diseased fish were stressed,the secreting activity of type Ⅲ and Ⅳ mucous cells was more exuberant.The surface of epidermal tumor was covered with mucus which formed white mucus layer.The empty spaces and holes were left after the lyses of mucous cells.Type Ⅲ mucous cell was largest in size(19.02±3.21 μm×14.42±2.69 μm);Type Ⅳ mucous cell was second(15.97±3.31 μm×12.96±2.81 μm);Type Ⅱ mucous cell was third(13.35±3.81 μm×11.05±3.00 μm);Type Ⅰ mucous cell was smallest(11.73±2.45 μm×7.71±0.97 μm).There was significant difference in sizes between different types of mucous cells.