Kuy, also known as Kui, Suay or Kuay (Thai: ภาษากูย; Khmer: ភាសាកួយ), is a Katuic language, part of the larger Austroasiatic family spoken by the Kuy people of Southeast Asia.

Kuy is one of the Katuic languages within the Austroasiatic family. It is spoken in Isan, Thailand by about 300,000 people, in Salavan, Savannakhet and Sekong Provinces of Laos by about 64,000; and in Preah Vihear, Stung Treng and Kampong Thom Provinces of northern Cambodia by 15,500 people.

Spelling variants and varieties include the following (Sidwell 2005:11).

Van der haak & Woykos (1987-1988) identified two major Kui varieties in Surin and Sisaket provinces of eastern Thailand, Kuuy and Kuay. Van der haak & Woykos also identified the following divergent Kui varieties in Sisaket Province, Thailand.

Mann & Markowski (2005) reported the following four Kuy dialects spoken in north-central Cambodia.

A variety of Kui/Kuy called Nyeu (ɲə) is spoken in the villages of Ban Phon Kho, Ban Khamin, Ban Nonkat, Ban Phon Palat, and Ban Prasat Nyeu in Sisaket Province, Thailand. The Nyeu of Ban Phon Kho claim that their ancestors had migrated from Muang Khong, Amphoe Rasisalai, Sisaket Province.

In Buriram Province, Kuy is spoken in the 4 districts of Nong Ki, Prakhon Chai, Lam Plai Mat, and Nong Hong (Sa-ing Sangmeen 1992:14). Within Nong Ki District, Kuy villages are located in the southern part of Yoei Prasat (เย้ยปราสาท) Subdistrict and in the western part of Mueang Phai (เมืองไผ่) Subdistrict (Sa-ing Sangmeen 1992:16).

The following is the phonology of the Kui (Surin) language: