Khlong Yai (Thai: คลองใหญ่, pronounced [kʰlɔ̄ːŋ jàj], lit: 'big canal') is a district (amphoe) of Trat province, eastern Thailand.

[1] In 1904, most of Patchan Khiri Khet, including Trat, was ceded to France in exchange for the French returning Chantaburi to Siam.

Shortly thereafter, France returned Trat and Klong Yai to Siam in exchange for Siem Reap and Battambang, which had been under Thai rule since 1795.

From 1979 to July 1986, the district was the site of a Thai Red Cross refugee camp, now called "Ratchakarun Centre", for Cambodians fleeing the fighting between the Khmer Rouge and the invading Vietnamese in the Cambodian-Vietnamese War.

An international border crossing with Cambodia is at Hat Lek village at the south end of the district, called the Khlong Yai Immigration Checkpoint.