Tou Yuan or Tuó Huán (Chinese: 陁洹国、 陀洹国) or Zhēn Tuó Huán (真陀洹、真陁洹) or Nòu Tuó Huán (耨陀洹) or Rù Tuó Huán (褥陀洹) was a short-lived ancient Mon political entity that existed in the present-day Lopburi province in central Thailand before the establishment of the Lavo in 648. It was annexed to Dvaravati in 647. Before the annexation, a local fable says Dvaravati at Kamalanka possible established royal relation with Qiān Zhī Fú at Si Thep, making Tou Yuan faced the two allied monarchs; Dvaravati to the south and Qiān Zhī Fú to the north.

It was the Mon's settlements, bordered Dvaravati to the southeast. Record of the Sui dynasty, which ruled China in 581–618 CE, says Tou Yuan fought many wars against Zhenla, who, at the same time, also had a conflict with Línyì to the northeast. The warfare between Chenla and Tou Yuan's successor state, Dvaravati's Lavo, continued into the Tang period. Certain battles may have been associated with the wars between Lavo and its northern sister Monic kingdom, Haripuñjaya, occurring in the early 10th century.

In contrast, Zhenla established peace relations via royal intermarriage with two other neighbors, Zhū Jiāng — which is identified as one of the Dvaravati-influenced polities — and Cān Bàn. However, Cān Bàn later became Zhenla's vassal, until the disintegration in the late 7th century, when it instead was under Wen Dan.

According to the details given in the Chinese leishu, Cefu Yuangui, compiled during the Song dynasty (960–1279 CE), Tou Yuan was situated southwest of Linyi in the middle of the sea and is bordered by Duohuoluo (墮和羅; Dvaravati), and met the kingdom of Duō Miè (多蔑国) to the west. It is a three-month and several days journey from Jiaozhi (交趾). Geoffrey Goble speculates it is possibly on the Malay peninsular, whereas Lawrence P. Briggs located it in the east of Thailand near the present-Chanthaburi. A Japanese scholar, Tatsuo Hoshino, identified Tou Yuan with Lopburi before the establishment of Lavo Kingdom in 648 and placed an early Dvaravati in the Bang Pakong Basin in eastern Thailand. Dvaravati expanded its influence to the Lavo in 648 and later to Canasapura's Mueang Sema [th] in the 8th century. The political center of Dvaravati in the eastern plain was then moved to a newly established Lavo Kingdom, while the western part was centered at Kamalanka's Nakhon Pathom.

Tou Yuan became the vassal of Dvaravati in 647. It sent envoys to the Chinese court several times between 644 and 647. In 647, Tou Yuan present a white parrot and baros ointment as tributes to China, yet they requested horses and copper bells and there was an edict granting them both. Its king's surname is Chashili 察失利 and his given name is Pomopona 婆末婆那.

The land is without silkworms and mulberry. They make clothes of lustrous white and rosy dawn-colored cloth. They have rice paddies, barley, hemp, and legumes. They raise white elephants, cows, sheep, and swine. Their custom is that everyone lives in elevated buildings (樓) called ‘dry pavilions’ (ganlan 干欄).

When their relatives die they do not eat in their room. After cremating the corpse they pick out the cremains and wash them in a pool. Thereafter, they will eat.