Meretrix meretrix Linnaeus is an important cultivated mollusk in north China. As a series of studies, which have been carried out since 2001, the mucous cells in the alimentary tract of M. meretrix were examined with histology and histochemistry methods by the light microscopy. The aim was to offer theoretical evidence for the studies of digestion and the culture of M. meretrix. The distribution of mucous cells in the alimentary tract was revealed by hematoxylin and eosin（ H. E） dyeing method, which indicated that the mucous cells were distributed in all of the digestive organs including labella, mouth, esophagus, stomach, intestines, rectum, etc, and mostly existed in epidermis. Only a small quantity of mucous cells existed in connective tissue of labella. The types and distributions of mucous cells were observed and analyzed also by AB-PAS（alcian blue and periodic acid Schiff＇s reaction, AB pH 2.5） dyeing method. Based on the observations, the mucous cells belonged to four types： type Ⅰ, pure red, PAS positive and AB negative, the cells included neutral mucopolysaccharide; type Ⅱ, pure blue, PAS negative and AB positive, the cells included acid one; type Ⅲ, PAS positive more than AB, the cells included mixed mucopolysaccharide, more neutral than acid, and type Ⅳ, AB positive more than PAS, these cells included mixed mucopolysaccharide, more acid than neutral ones. The statistic results showed that, in different parts, the mucous cells had different types and densities. There was a small quantity of mucous cells in labellurn, and most of them existed in the ruga part. The types of the mucous cells of labellum were types Ⅱ and Ⅳ. There were large quantities of mucous cells in esophagus, which belonged to all four types. There were more mucous cells in stomach than in labellurn, but less than in esophagus. The mucous cells include four types, and the distribution of the mucous cells is dispersed. The mucous cells in intestines increase dramatically. Most mucous cells lie in the rectum, consisting of types Ⅱ, Ⅲ, and Ⅳ. By the studies of AB - PAS （AB, pH1. 0）, it was found that the mucus included neutral mucopolysaccharide, and acid one that included sulphate mucopoiysaccharide and carbonic mucopolysaccharide. The most competent of acid mucopolysaccharide in labella and rectum was carbonic mucopolysaccharide, only a little was sulphate mucopolysaccharide. In addition, the mucous cells had acid phosphoataes （ACP） and alkaline phosphoataes （AKP） activity, but the activity was weak. Our work exhibited that the mucus released from mucous cells had the activity of ACP and AKP.