A header box includes a first bottom plate and an unperforated cover plate. The first bottom plate includes a first surface and a second surface opposite to the first surface. The first bottom plate is of a one-piece configuration. The first surface is recessed inwardly to form a straight first hole extending along a length direction. The second surface is recessed inwardly to form at least two straight second holes extending along a width direction perpendicular to the length direction. The first hole is communicated with the at least two second holes. The cover plate is connected to the first surface to block an opening of the first hole on the first surface. A heat exchanger having the header box is also disclosed.