Si Thep Historical Park (Thai: อุทยานประวัติศาสตร์ศรีเทพ) is an archaeological site in Thailand's Phetchabun province. It covers the ancient city of Si Thep, a site inhabited from around the third to fifth century CE until the thirteenth century, spanning cultural periods from late prehistory, through Dvaravati, to the golden age of the Khmer Empire. Si Thep was one of the largest known city-states that emerged around the plains of central Thailand in the first millennium, but became abandoned around the time the Thai-speaking cities of Sukhothai and later Ayutthaya emerged as new centres of power in the Chao Phraya River basin.

The site gained the attention of modern archaeology in 1904 following surveys by Prince Damrong Rajanubhab, and it was listed as an ancient monument in 1935. The Fine Arts Department has undertaken continued study and excavations of the site, which has also been studied by archaeologists Prince Subhadradis Diskul, H. G. Quaritch Wales and Jean Boisselier, among others.

As per historical evidence found on the site, Si Thep was possibly the center of the Dvaravati mandalas. Via royal intermarriage, it was also considered the sister city of Sema, the capital of the neighboring state, Canasapura, located eastward on the opposite side of the Dong Phaya Yen Mountains in the Mun River basin. Some scholars believe Si Thep was Ayojjhapura, the predecessor to Ayodhya, mentioned in the Pali chronicles Ratanabimbavamsa and Jinakalamali.^: 51

Si Thep was listed as a historical park in 1984 and was proposed as a tentative UNESCO World Heritage Site by Thailand in 2019. On 19 September 2023, it was inscribed on the World Heritage List as The Ancient Town of Si Thep and Its Associated Dvaravati Monuments. It is Thailand's first successful cultural World Heritage Site nomination since Ban Chiang in 1992.