The Nauru government and donor agencies are to upgrade the island's Aiwo harbour.
The development will mean Nauru has a fully functioning harbour for the first time.
The ADB is to provide a grant of $US21.3 million to the project with the Green Climate Fund and Australia to contribute $US26.91 million and $US14.08 million respectively, Nauru itself will put up $US17.3 million.
Meanwhile Japan will support the project by supplying port operation equipment.
The Australian high commissioner to Nauru, Angela Tierney, said the new port will create jobs and spur economic growth through increased trade and investment in Nauru.