| Official Name: | Khlong Yai |
| Pushpin Map: | Thailand |
| Settlement Type: | Town |
| Subdivision Type: | Country |
| Subdivision Name: | Thailand |
| Subdivision Type1: | Provinces |
| Subdivision Name1: | Trat Province |
| Subdivision Type2: | District |
| Subdivision Name2: | Khlong Yai District |
| Population Density Km2: | auto |
| Coordinates: | 11.775°N 102.8675°W |
| Elevation M: | 6 |
| Timezone: | ICT |
| Utc Offset: | +7 |
Khlong Yai is a town (thesaban mueang) in Trat Province in east Thailand, capital of the Khlong Yai District, of which it covers part of the tambon Khlong Yai. It is on the coast of the Gulf of Thailand near the border with Cambodia.
Khlong Yai is found on a thin strip of territory belonging to Thailand along the coast of the Gulf of Thailand. The border with Cambodia runs roughly parallel to the coast at a distance of roughly 2km (01miles), following the Cardamom Mountains. The high rainfall of the area results in dense rain forest along this narrow coastal strip. The hills nearest to Khlong Yai reach to about 300m (1,000feet), but further north the height of the mountains exceeds 1000m (3,000feet).
Khlong Yai has a tropical monsoon climate (Köppen climate classification Aw) influenced by the nearby Cardamom Mountains, which amplify the summer monsoon. While no month is truly dry, a short dry season runs from December to January. Rain increases somewhat from February to April, and then the main monsoon season begins in May, lasting until October. The monsoon season features torrential rain, with over 1000mm falling in August alone, and over 800mm falling in each of June and July. The rains ease in November, although significant rainfall may still occur. The highest monthly rainfall recorded from 1961 to 1990 was a total of 2072.4mm in August.
The main road in the area is Route 318, which runs up and down the coast. To the south it connect Khlong Yai to a border crossing to Cambodia at Hat Lek, not far from the Cambodian town of Koh Kong. To north the road connects to Trat, from which Route 3 (the Sukhumvit Road) leads to Bangkok.