Crown - of - thorns starfish (COT) is a benthic species and constitute as bioindicator of coral reef ecosystem. COT is one of the coral prendators which potentially becomes a very big problem in the coral reef ecosystem management. It would be very useful in the management of marine resource if we understand more about this species. This paper explains the biology and ecology (anatomy, toxicity,reproduction,life aycle,food,food system,growth,habitat) of COT.