Sanxia District () is a district in the southwestern part of New Taipei, Taiwan. It is the second largest district in New Taipei City by area after Wulai District.
The old name of Sanxia, Sa-kak-eng () dates back to the 1780s and refers to the meeting of the Dahan River, Sanxia River, and . In 1920, Taiwan's Japanese government administratively designated the town as , Kaizan District, Taihoku Prefecture.
The first Han people settled in what would become Sanxia during the 1700s, and originally rented land from the Plains Indigenous before forcing their displacement. After several groups of settlers from Southern China fought amongst themselves, Anxi County natives became dominant and began cultivating Strobilanthes cusia in the area. After Monga merchant Weng Tian introduced Indigofera tinctoria to Sa-kak-eng, the production of indigo increased, with the first recorded instance of large-scale production dating to 1822. Lin Tzu-tzeng of Anxi moved to Sa-kak-eng in 1830, and established the town's first dyeing workshop.
After the first coffee plants on Taiwan were imported by the British to Tainan in 1884, the first significant small-scale cultivation took place in Sa-kak-eng.
On December 25, 2010, Sanxia Township was renamed Sanxia District as Taipei County became a special municipality, New Taipei City.
It has an area of 191.45 km<sup>2</sup> and a population of 115,443 (February 2023).
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