Nauru is exporting a barge load of rocks to Tuvalu.
It is sending 5000 metric tonnes of rocks to Tuvalu to help with coastal protection around the reclaimed Queen Elizabeth II national park on Funafuti.
The trade followed an agreement signed during the Pacific Forum summit in September.
Nauru's President Baron Waqa said the sale would not affect his country's coastal protection work.
He said Nauru had all the rocks Tuvalu needed.
The sale was paid for with funding through the Green Climate Fund.