Round goby (Neogobius melanostomus) spawning behaviour and parental care by males may be mediated by pheromones. We examined the spatial organization of the peripheral olfactory organ in round goby. Olfactory receptor neurons were visualized in cryostat sections stained for acetylated tubulin immunocytochemistry and by transmission electron microscopy. The olfactory epithelium is located adjacent to the tentacular anterior nostril and extends ventrocaudally along the relatively flat surface of the nasal cavity. Numerous nonmyelinated nerve fascicles formed in the lamina propria and converged into a prominent olfactory nerve. A sac-like enclosure was found on the posterior ventral surface that may regulate flow through the nares.