A cover window includes a first layer having a first modulus, a second layer disposed on the first layer and having a second modulus smaller than the first modulus, and a third layer disposed on the second layer and having a third modulus equal to or larger than the first modulus, and in which the third layer includes a nanoparticle-polyurethane complex in which polyurethane is bonded with nanoparticles by a covalent bond. Therefore, the cover window of the present disclosure provides effects that the folding and rolling are possible with excellent surface characteristic and the restorability against the pressing and excellent optical property. A flexible display device may include the cover window.