Abstract: The morphological structure of pineal body of Carassius auratus was observed by lightand electron microscopy.It was found that besides a pineal body composed of a dorsal sacand a pineal duct in the fold of the sac,C. auratus also possesses a degenerated paraphysisand a parapineal body.The dorsal sac has a single layer of ciliary columnar cells and its lumen connects with the third brain ventricle.The pineal duct is mainly composed of photoreceptor cells,supportive cells,ganglion cells,many blood vessicles and unmyelinated nerve fibers.The pineal body is not only a photoreceptor organ but also an endocrine gland.