Abstract: This paper researched the histology and enzymic histochemistry during the pearl sac formation of Anodonta woodiana Lea, with the methods of H·E dyeing andenzymic histochemistry. It is proved that during the pearl sac formation, the primordial pearl sac epithelial cells formed and degenerated, then the secondary pearlsac epithelial cells, which are suggested to come from the connective tissue of therecipient mussel, formed after that. The activities of nine kinds of enzymes chan-ged in different places of the pearl sac and recipient mussel during different periodof pearl sac formation, which means that the formation of pearl sac is a very complicated physiological and biochemical process relating to energy metabolism、material metabolism、material transfer, and so on.