Olfactory organ is one of the important chemical sensory organs in fish, which plays an important role in foraging, reproduction and migration. In order to understand the structure and early development characteristics of olfactory sac of Siniperca chuatsi, the morphological structure of olfactory organ, structure and early development of olfactory epithelium were observed by paraffin section, H.E staining, Massorn staining, immunohistochemistry, scanning and transmission electron microscopy. The results showthat Siniperca chuatsi has two pairs of nostrils, and the anterior and posterior nostrils are closely linked, with flaps (Fig. 1a). The olfactory sac is located in the olfactory cavity, which is composed of 16﹣20 primary olfactory lamellas (Fig. 1b). It is a G-type olfactory sac, and the primary olfactory lamellas generate secondary olfactory lamellas through folds (Fig. 1c). The distal edge of olfactory lamella is a non-sensory area, and the sensory area is mainly located at the middle and proximal ends of olfactory lamellas. Olfactory epithelial cells can be divided into six categories: ciliated non-sensory cells, ciliated receptor cells, microvilli sensory cells, supporting cells, basal cells and mucous cells (Fig. 1e﹣g). Under the scanning electron microscope, there are a large number of cilia coverings on the surface of sensory area, and microvilli on the surface of secondary olfactory lamellas (Fig. 1h, i). There are convex ridges on the surface of the non-sensory region (Fig. 1j). From larvae to young fish, the olfactory substrate of 1﹣7 days old larvae is thin and the cells are loosely arranged (Fig. 2a). At 7 days of age, the olfactory base plate is thickened to form an olfactory fossa with cilia on the surface of olfactory epithelium (Fig. 2b). At 10 days of age, the olfactory base continues to sink into the olfactory fossa and forms an olfactory cavity (Fig. 2c). At 26 days old, juveniles form the first pair of primary olfactory lamellas (Fig. 2e), and at 55 days old, juveniles form eight pairs of primary olfactory lamellas (Fig. 2h). Before 55 days of age, the olfactory sac of S. chuatsi develops slowly, the primary olfactory lamellas are arranged laterally, and the secondary olfactory plate is not formed.