A blow molding toolbox has a casing, a cover, and multiple reinforcing elements. The casing has multiple connecting recesses, multiple guiding slots, and multiple positioning recesses. The connecting recesses are deposited on an external surface of the casing at corners of the casing. The cover is pivotally connected to the casing and has a same structure as the casing. Each one of the reinforcing elements is connected to the casing at one of the corners of the casing to cover a corresponding connecting recess of the casing or is connected to the cover at one of the corners of the cover to cover a corresponding connecting recess of the cover, and each reinforcing element has a body, at least one fixing tube, and at least one tapping screw. The reinforcing elements may increase the structural strength of the blow molding toolbox.
