Abstract: A knockdown bed liner assembly for pickup-type trucks comprising interconnectable floor, side and front panels, and a separate tailgate panel. The floor and side panels are shaped to accommodate the wheel wells of a truck, and the floor panel is provided with a unique rib construction to facilitate movement of cargo on the panel and to permit air circulation between the floor panel and the truck bed floor to protect against condensation and rust. The panels are packaged and shipped in knockdown form in a relatively compact easy-to-handle container ready for assembly at the point of use.