A variable light transmittance window includes: a substrate configured to transmit light; a thermochromic layer on the substrate; first function thin film layers on opposite surfaces of the thermochromic layer; and second function thin film layers on respective surfaces of the first function thin film layers opposite the thermochromic layer, wherein a difference between refractive indices of the first function thin film layers and the second function thin film layers is greater than a difference between refractive indices of the first function thin film layers and the thermochromic layer.