Si Wichian (Thai: สีวิเชียร) is a capital tambon (subdistrict) of Nam Yuen district, in Ubon Ratchathani Province, Thailand.

[1] Neighbouring subdistricts are (clockwise from the west) Song, Bu Pueai, and Dom Pradit, as well as Choam Khsant District of Cambodia in the south.

[2][3][5] Si Wichian gained tambon (subdistrict) status in 1981 by absorbing seven other villages located in the Song's eastern area.

[8] After its establishment, Tambon Si Wichian was administered by two different local governments, including the Sukhaphiban Nam Yuen (สุขาภิบาลน้ำยืน), founded in 1973, which governed a populous area in the district's town center and covers some parts of Song and Si Wichian,[9] and the Subdistrict Council of Si Wichian, which covers the tambon's remaining area.

[1] The area is shared by two local governments; the district's town center is governed by the Nam Yuen Subdistrict Municipality (เทศบาลน้ำยืน, Nam Yuen Township), which also governs some of the neighboring subdistrict, Song, while the remaining area is covered by the Si Wichian Subdistrict Municipality (เทศบาลตำบลสีวิเชียร, Si Wichian Township).