| Official Name: | Khlong Ton Sai |
| Native Name: | คลองต้นไทร |
| Settlement Type: | Khwaeng |
| Coordinates: | 13.7221°N 100.5088°W |
| Subdivision Type: | Country |
| Subdivision Type2: | Province |
| Subdivision Name2: | Bangkok |
| Subdivision Type3: | Khet |
| Subdivision Name3: | Khlong San |
| Area Total Km2: | 1.773 |
| Area Footnotes: | [1] |
| Population As Of: | 2020 |
| Population Total: | 18,704 |
| Timezone: | ICT |
| Utc Offset: | +7 |
| Postal Code Type: | Postal code |
| Blank Name: | TIS 1099 |
Khlong Ton Sai (Thai: คลองต้นไทร, in Thai pronounced as /kʰlɔ̄ːŋ tôn sāj/) is a khwaeng (subdistrict) of Khlong San District, in Bangkok, Thailand. In 2020, it had a total population of 18,704 people.[2]
The name of the subdistrict, called after the natural khlong (canal) that run through the lower part of area, "Khlong Ton Sai". Its name means "Canal of Figs" because there were many trees of this type growing along the waterways in the past.
In the era before 1957, Khlong Ton Sai was a clear and clean watercourse and was a thoroughfare for people to travel around. It was a path connects the Chao Phraya River with Khlong Bang Sai Kai in the neighbouring Thon Buri area. Currently, the canal is shallow, has polluted water, and is shorter in distance than in the past.