Diplomatic ties with Taiwan and would instead recognise China, according to a government post on social media.
President David Adeang announced the decision in a national address posted to an official Facebook page, explaining "the Nauru government's decision to recognise the People's Republic of China".
In a media release, the Nauru government said it would no longer recognise Taiwan "as a separate country" but "rather as an inalienable part of China's territory".
The release added that Nauru would "sever diplomatic relations" with Taiwan immediately, and would "no longer develop any official relations or official exchanges with Taiwan".
The decision will likely be seen as major coup for Beijing -- Nauru was one of the few nations to officially recognise Taiwan on a diplomatic basis.
Only 12 states, including the Holy See, now fully recognise Taiwan.
Nauru has a population of around 12,500 people, and is the latest Pacific country to turn its back on a longstanding relationship with Taiwan.
In 2019, Solomon Islands similarly announced that it was switching diplomatic recognition from Taiwan to China.
In Africa, only Eswatini officially recognises Taiwan, while in Latin America, seven states have full diplomatic ties with the island, including Belize, Guatemala, Haiti and Paraguay.