Saek (Sek; Thai: ภาษาแสก) is a Tai language spoken in at least ten villages in Khammouane Province, Laos, and at least four villages in Nakhon Phanom Province in northeastern Thailand, just across the Mekong River. It is spoken by the Saek people.

The Saek tones are (Hudak & Gedney 2010):

Saek tonal splits are as follows (See Proto-Tai language#Tones for clarification.).

Saek is spoken in the following locations (Hudak & Gedney 2010:251-252).

Two Saek villages are "Ban Asamat" and "Ban Phai Lom," located just off the main river road a few kilometers north of Nakhon Phanom city. Another is Ban Ba Wa Saek, located further upriver, but inland a few kilometers. However, except for the older generation, the Saek language is all but disappearing as there is a strong tendency for younger generations to use the local trade language Lao/Isan, and/or the official Central Thai language as they are assimilated into mainstream Thai society.

William Gedney lists the following Saek villages in Nakhon Phanom Province, Thailand.

According to Gedney, abandoned Saek villages in Thailand include:

According to Gedney's texts and notebooks, Saek is spoken in the following locations in Laos.