Ouaddai ( Larabci: وداي‎ ) yanki ne na Chadi, wanda ke kudu maso gabashin ƙasar, tare da babban birninta a Abéché . Kafin shekara ta 2002 an san shi da lardin Ouaddaï ; a cikin 2008 an raba bangarorin kudu na Ouaddaï ( Sashen Sila da Djourf Al Ahmar Department ) don zama sabon Yankin Sila (wanda aka fi sani da Dar Sila). Yankin shi ne asalin tsohuwar Daular Ouaddai, ko Masarautar Wadai, wanda ya wanzu daga farkon ƙarni na 16 har zuwa 1911 lokacin da Faransa ta ci ta a yakin Ouaddai . Duk manyan biranen daular - Ouara (wanda yanzu ba kowa) da Abéché - suna cikin yankin Ouaddaï na zamani. Yankin yana iyaka da yankin Wadi Fira daga arewa, Sudan ta gabas, yankin Sila a kudu, da yankin Batha zuwa yamma. Yankin ƙasa gaba ɗaya shimfida savannah ne, yana ɗan tashi zuwa gabas inda tsaunukan Ouaddaï suke. Abéché babban birni ne na yankin kuma shine birni na huɗu mafi girma a cikin Chadi; sauran manyan matsugunan sun haɗa da Abdi, Adré, Am Hitan, Bourtail, Chokoyan, Hadjer Hadid, Marfa, Mabrone da Tourane.