Original Chiangmai Sign Language
- Language: Original Chiangmai Sign Language
- Alternate names: Chiengmai Sign Language, Original Chiangmai Sign Language, Old Chiangmai Sign Language, OCMSL
- Language code: csd
- Language family: Deaf sign language (SIL classification)
- Number of speakers: ~19
- Vulnerability: Endangered
"OCMSL is a original sign language that developed among deaf people living in Chiang Mai in the North of Thailand long before the first school for deaf people was established in 1951." (Woodward and Wongchai, 2015) This language family includes original sign languages in Thailand and Hai Phong Sign Language.