The 23-year-old France youth international has made just 16 appearances for the Black Cats since his arrival from another Turkish club, Bursaspor, in a £3.8million deal in January.
N'Diaye's move continues the changes being made by new manager Paolo Di Canio at the Stadium of Light.
The Italian has made nine new signings this summer and allowed six players to leave permanently while Danny Graham, and now N'Diaye, have moved out on loan.
A statement on the Sunderland website read: "Alfred N'Diaye has joined Eskisehirspor on a season-long loan. The 23-year-old returns to Turkey having arrived at the Stadium of Light from Bursaspor during the January transfer window."