Ofo (/ˈoʊ.foʊ/ OH-foh), also known as Mosopelea, is a language formerly spoken by the Ofo people, also called the Mosopelea, in what is now Ohio, along the Ohio River, until about 1673. The tribe moved south along the Mississippi River to Mississippi, near the Natchez people, and then to Louisiana, settling near the Tunica.

In the 18th century, the Mosopelea were known under the names Oufé and Offogoula. On the basis of the presence of the phoneme /f/ in these names, early linguists once suspected that Ofo was a Muskogean language. However, anthropologist John R. Swanton met an elder Ofo speaker, Rosa Pierrette, in 1908 while he was conducting fieldwork among the Tunica. From her information, he was then able to confirm that the language was Siouan and was similar to Biloxi. Pierrette had spoken Ofo as a child, but Swanton says she told Albert Gatschet that the rest of her tribe "had killed each other off" when she was 17.

Ofo follows a process similar to Grassmann's law, with /h/ counting as an aspirated consonant: /oskʰa/ 'crane' + /afʰã/ 'white' > /oskəfʰa/ 'white egret' and /apʰeti/ 'fire' + either /təsʰihi/ 'to burn' or /təsʰihi/ 'to breathe' > /apesʰihi/ 'smoke'.

The inventory is as follows:

All vowels, including /ə/, may bear stress.

Ofo is considered to be a mildly polysynthetic language.

Ofo distinguishes between alienable and inalienable possession by the use of a prefix for first-, second-, and third-person singular as well as first-person dual. That can be abbreviated to 1sg, 2sg, 3sg, and 1du, respectively. The alienable possessions include the following: 1sg {ba-, aba-}, 2sg {č-, ača-}, 3sg {}, 1du {ã-}. The inalienable possessions include the following: 1sg {mi-}, 2sg {čĩ-}, 3sg {ĩ-}, 1du {ã-}.

Ofo uses the enclitic suffix -ni, to demonstrate negation. That enclitic is usually after the predicate.