Tha Pho Si (Thai: ท่าโพธิ์ศรี) is a tambon (subdistrict) located in the central region of Det Udom District, in Ubon Ratchathani Province, Thailand.

[2] Neighbouring subdistricts are (clockwise from the south) Top Hu, Non Sombun, Na Charoen, Mueang Det, and Klang.

[1] The area was first settled in the late 1800s, with the first village, Bak Waeng (บักแหว่ง), governed by Mueang Det, the district capital.

[1] The settlement was eventually renamed "Tha Pho Si" in 1902, after the giant sandbox tree (Thai: โพธิ์ศรี; Pho Si) that was founded near the waterfront pavilion on the bank of the Lam Dom Yai River.

[1] The Tha Pho Si subdistrict was formed in 1976 by combining two areas splitting from Mueang Det and Klang, which consisted of five and one villages, respectively.