Abstract: A ventilated seat cover apparatus includes an understructure assembly which includes a pair of side pipe assemblies and a plurality of transverse pipes connected between the side pipe assemblies. The transverse pipes include plural air-venting apertures, and the side pipe assemblies include end portions which have removable and replaceable pipe plugs. A porous understructure-cover sheet covers the understructure assembly, and a flexible hose is connected to the understructure assembly. Cushion units are placed between neighboring transverse pipes. The understructure assembly may include a seat portion and a back portion connected to the seat portion by a pair of flexible interconnector hoses. Straps are used to connect the seat portion and the back portion to a seat and a seat back, respectively. The side pipe assemblies include sequential arrays of T-shaped members alternating with straight members.