Ouaddaï may refer to:

• Ouaddaï highlands, an area in eastern Chad along the border with Sudan
• Ouaddaï Prefecture, a former political prefecture of Chad
• Ouaddaï Region, a political region of Chad created in 2002
• Wadai Empire (1635–1912), a kingdom located to the east of Lake Chad
• Wadai War (1906-1911), between France and the Wadai Empire