Mr Jammeh said Gambia would remain a friend of Taiwan's people
Gambia has announced that it has cut diplomatic ties with Taiwan.
President Yahya Jammeh's office said the move was for reasons of "national strategic interest".
The West African state was one of a few African countries to recognise Taiwan, which China regards as part of its territory.
Correspondents say it is unclear if the move is linked to the development of relations with China, which has a growing influence in Africa.
Despite the announcement, Mr Jammeh said Gambia hoped to "remain friends" with the Taiwanese people.
"This decision has been taken in our strategic national interest," a statement from his office read, without elaborating.
"We are proud that we have been a very strong and reliable partner of the Republic of China [Taiwan] for the past 18 years, the results of which are there for every Taiwanese to see.
"Despite the end of diplomatic ties with Taiwan, we will still remain friends with the people of Taiwan."
Taiwan said it was surprised by Gambia's decision.
"Our government express shock and regret that Gambian President Yahya Jammeh sent a letter to our embassy in Gambia on 14 November to inform us [of] the immediate termination of ties," Vice Foreign Minister Simon Ko said in Taipei.
"We think this is Jammeh's personal decision," he added.
China has been investing heavily in Africa at it relies on the continent for oil and other natural resources.
China and Taiwan split in 1949, when the Chinese Communist Party overthrew the Republic of China (ROC) and founded the People's Republic on the mainland, forcing the ROC government to retreat to Taiwan. Beijing says Taiwan is an inalienable part of China.
Initially, most African states recognised the Taipei government but their number has steadily declined.
Gambia's decision means that Swaziland, Sao Tome and Principe and Burkina Faso are the only African countries that remain allies with Taiwan.
However, earlier this week officials in Sao Tome and Principe said China plans to open a trade mission to promote projects there.
It comes 16 years after Beijing broke off relations with the tiny Central African nation over its diplomatic recognition of Taiwan.