In a seat with ventilation property, at least one three-dimensional network cushion element is provided in a foam padding(s) of the seat at at least one point on which at least one body portion of a seat occupant is to be substantially contacted. The three-dimensional network cushion element is formed by a plurality of fibers, each being composed of a core portion and a sheath portion covering the core portion, such that all the fibers are bonded with one another at the respective sheath portions thereof. Preferably, each of the fibers may be an helical fiber of eccentric core type wherein the core portion is eccentrically positioned in the sheath portion. Further, the three-dimensional network cushion element(s) may be arranged in the foam padding so as to prevent intensive exertion of a load from the seat occupant's body portion(s) upon the three-dimensional network cushion element(s).