Morphology and histochemistry of gill of the abalone, Haliotis discus hannai were described using light microscopy and scanning electron microscopy (SEM). The abalone has bipectinate gill of protobranch. The cilia and microvilli were well-developed on the free surface of the gill filaments. The epithelial layer of gill filament was simple and composed columnar epithelia and mucous cells. Result of AB-PAS (pH 2.5 and 1.0) and AF-AB (pH 2.5) reaction showed that mucous cells contained mainly acidic carboxylated mucosubstances.