Oreonectes polystigmus is a cave-dwelling loach distributed in the karst area of Guangxi, China. Its olfactory organ plays an important role in its activities. We observed the olfactory epithelium of O. polystigmus by using a scanning electron microscope (SEM), in order to get more knowledge and data on its morphological adaptation to the subterranean river, an extreme environment for animals. The olfactory organs of O. polystigmus are oval in shape, lying in the olfactory chamber. The average length of olfactory sac is 1.24 mm, 1.36 times of eye diameter, which revealed that O. polystigmus is a kind of “olfactory sensation” fish. The olfactory apparatus has 22 to 24 primary lamellae arranged on both sides of a narrow raphe. Each lamella has developed tongue-like structure. Non-sensory cilia are continuously distributed on the lamellae, only a few on the area closed to the raphe, where has many folds with plenty of tiny pores. Sensory cilia mainly locate the area with thin non-sensory cilia. Microvilli are always distributed under non-sensory cilia. The number of pits on the middle lamellae is more than one on the anterior and posterior lamellae. And on the same lamella, pits on the place close to raphe are denser than ones on anywhere else. Bare and non-bare regions on the lamella and raphe always have a clear boundary. Non sensory cilia and microvilli on the raphe are basically distributed in the grooves of non-bare region. Area of bare region on the raphe is almost equal to one of non-bare region. Epithelium of raphe is formed to a series of polygons by continued microridges. Comparing to some surface fish, O. polystigmus has dense non sensory cilia and a certain amount of sensory cilia and micro villi on the lamella and raphe, which are clearly typical characters adapted to the dark environment. Moreover, isosmate is the hydrodynamic mechanism for O. polystigmus, revealing its adaptation from another angle.