Reproductive behaviours of the rockhopper blenny Andamia tetradactyla were studied on supralittoral reefs of Kuchierabu-jima Island, southern Japan. Territorial males defended mating nests, which were situated around crevices between rocks and concentrated in the high intertidal zones near the vertical limits of waves. Females occurred in large numbers on algal mats around wave-splashed zones, and approached the nests on both rising and falling tides during daytime. Courtship displays occurred on both rising and falling tides, especially when waves surged and sprayed on the nests. Females spawned eggs in a single layer on air-exposed rock surfaces inside nests. Andamia tetradactyla did not mate in the tidal conditions in which nests were either underwater or completely dried up. Territorial males stayed all day in the nests to guard eggs, even though nests emerged above water for c. 12 h each day. Thermo-hygrometer analysis showed that nests maintained higher humidity than outside. Patterns and sequences of the mating behaviours of fishes do not seem very different from those of underwater blenniid fishes. Thus, A. tetradactyla maintains reproduction out of water, retaining humid habitats on supralittoral reefs, in mating styles that are probably not drastically changed from their ancestral blenniid fishes.