Seventh Day Adventist Church of Tonga, Church building in Nukuʻalofa, Tonga.

The Seventh Day Adventist Church of Tonga (Tongan: Siasi ʻAhofitu) is a small church in Nukuʻalofa. Its first chapel was a prefabricated building brought by the Pitcairn mission ship in June 1899; after 18 months it was dismantled and rebuilt as a church measuring 5 by 10 metres. Missionary doctor Merritt Kellogg built a timber home at Magaia that long housed the mission superintendent.

Adventist missionaries E. H. Gates and A. J. Read visited Tonga in June 1891 aboard the Pitcairn, and Edward Hilliard settled in Nukuʻalofa on 30 August 1895. The first Tongan church was organized on 10 September 1899, when Englishman Charles Edwards was baptized. The church was revitalized in 1912 through renewed evangelism and resumed its educational strategy in 1922, which increased conversions.

The church manages sixteen congregations across Tonga, offering services in the Tongan language and maintaining strong connections with local educational institutions.

The church is located in central Nukuʻalofa and is accessible on foot from many nearby areas. Visitors should note that services occur on Sundays due to the island's position east of the International Date Line.

Because Tonga lies east of the 180° meridian but west of the International Date Line, Adventists here keep the Sabbath on Sunday, treating the date line as if it ran along 180° and the zone as UTC−12:00.