Although decorating behaviour is widely reported as a predator avoidance strategy among marine crabs, few studies have provided experimental evidence for this. Significance of decorating behaviour of the majid crab Tiarinia cornigera as antipredator response was examined by the field tethering and laboratory experiments. Survival of decorated crabs was significantly higher than that of non-decorated crabs after two days in an intertidal rock pool. In a laboratory experiment, crabs used more algae for decoration in the presence of predators (puffer fish) than when predators were absent. These data demonstrate that T. cornigera decorates with algae in response to predators to reduce predation pressure.