The aim of this short review is to contrast available data on urate function in aquatic and terrestrial crustaceans. Uric acid is known to be an alternative to ammonia for nitrogen excretion when water availability is reduced. Uric acid deposits have been observed in the hemocoel of many terrestrial or semi-terrestrial species and it makes up to 80% of excreted nitrogen in the most terrestrial decadpod, the robber crab Birgus latro. On the other hand, some aquatic species although they are ammonotelic, can produce small amounts of urate. This molecule plays a role in oxygen transport by enhancing oxygen binding to hemocyanin in situations such as hypoxia, temperature increases or emersion.