Abstract: In this paper, changes of mucous cells in the early developmental stage of carp, Cyprinus carpio, were studied by the method of histochemical techniques-a combination of Alcine Blue staining under acid conditions and PAS reaction. The mucous cells were first Observed in hatching glands at the 1st day before hatching. They appeared immediately in the mouth cavity, pharynx, gills and gut after hatching. With the development of the carp, the density, type and content of mucous cells increased and became complicated. Type I and Type IV of mucous cells containing unitary mucoitin are in immature stage and appeared earlier than Type II and Type III which are in mature stage and contain multiple mucoitins. The mucous cells mainly distributed in mucousal epidermis of such organs as skin.mouth.gill and intestine.