Abstract: We studied the histological structure and histochemistry in the digestive tract of Siganus oramin by using HE and AB-PAS in this paper. Results show that S.oramin has comparatively small orpharyngeal cavity, with slight teeth on maxillary, short and closely arranged teeth on mandible, no tooth on vomer, palatine bone and tongue, soft and slight upper pharyngeal teeth, slight oesophagus, and the V-shaped stomach. 5~6 pyloric caeca are found on the intestine. Ratio of intestine length to body length is 2.73. The gastric gland is developed and pipe shaped, opening to the gastric pit. Height of mucosa membrane pleats lowers on pyloric stomach and villous processus-like structure occurs on the pleats. There are abundance mucosa pleats on the surface of foregut, and plenty of vacuole-like goblet cell. According to AB-PAS, 4 types of the mucous cells in the digestive tracts of S.oramin are observed: TypeⅠis red, TypeⅡ is blue, Type Ⅲ is purple reddish, and TypeⅣ is blue purple. Most of mucous cells in oesophagus are of Type Ⅱ and Type Ⅲ, and those in stomach, intestine and pyloric caeca are of Type Ⅱ and Type Ⅳ. The density of mucous cells in hindgut are found to be TypeⅡ>Type Ⅲ>TypeⅣ. The ratio of Type Ⅱ to mucous cells is the biggest in midgut and hindgut.