Gongduk or Gongdu (Tibetan: དགོང་འདུས་, Wylie: Dgong-'dus, it is also known as Gongdubikha) is an endangered Sino-Tibetan language spoken by about 1,000 people in a few inaccessible villages located near the Kuri Chhu river in the Gongdue Gewog of Mongar District in eastern Bhutan. The names of the villages are Bala, Dagsa, Damkhar, Pam, Pangthang, and Yangbari (Ethnologue).

The people are said to have come from hunters that would move from place to place at times.

The language is notable for only being discovered by linguists in 1991. Currently, George van Driem is working towards the completion of a description of Gongduk based on his work with native speakers in the Gongduk area.

Gongduk has complex verbal morphology, which Ethnologue considers a retention from Proto-Tibeto-Burman, and is lexically highly divergent. On this basis, it is apparently not part of any major subgroup and will probably have to be assigned to its own branch.

George van Driem (2001:870) proposes that the Greater Bumthang (East Bodish) languages, including Bumthang, Khengkha, and Kurtöp, may have a Gongduk substratum. Gongduk itself may also have a non-Tibeto-Burman substrate.^{[citation needed]}

Gerber (2018) notes that Gongduk has had extensive contact with Black Mountain Mönpa before the arrival of East Bodish languages in Bhutan. Gongduk also has many Tshangla loanwords. The following comparative vocabulary table from Gerber (2020) compares Gongduk, Black Mountain Mönpa, and Bjokapakha, which is a divergent Tshangla variety.

Gongduk has productive suffixal morphology (van Driem 2014).

Examples: