Police in Zanzibar seized 1041 elephant tusks hidden in a container of anchovies on Tuesday.
Police chief Martin Lissu said the consignment was offloaded at the port two weeks ago and stored in outskirts of Stone Town.
Two transport agents are being held in connection with the discovery.
Mr Lissu said the shipment appeared to have been destined for Malaysia, and purportedly originated from the mainland Tanzanian port of Dar es Salaam.
The tusks represent the death of more than 500 animals. They were packed in a container of dried anchovies.