Optical microscopy and transmission electron microscopy were used to investigate the microstructure and ultrastructure of the gill and gill lamellae in Zebrafish (Danio rerio). There are four pairs of holobranches, and the gill rakers are prick-shaped, primary lamellae are arranged in a comb-like pattern on the gill arch, and secondary lamellae are evenly arranged on both sides of the primary lamella (Fig. 1). Secondary lamella consists of pillar cells, epithelial cells, endothelial cells and capillary network. Chloride cells are distributed mainly over the base of primary lamellae and perivascular area, and they contain abundant mitochondria and excretory vesicles. The cells can be divided into two subtypes according to their morphological characteristics and electron density. Mucus cells usually co-exist with chloride cells, and they often appear to be open at the surface between adjacent epithelial cells. The Zebrafish gill structure, which is closely related to its function, is similar with that of other teleost fish (Fig. 2).