To provide mat foundation for a dwelling house, and a construction method thereof in which it can be constructed easily, speedily, and with stable quality without requiring skillfulness.

Sand 27 is horizontally placed on the ground at a construction site, a number of mat slabs 1 of precast concrete having coupling bars 3a protruded from side end surfaces are disposed in parallel on the sand 27, and joint concrete is placed between the adjacent mat slabs 1 to embed the coupling bars 3a in joint concrete, so a single panel of mat foundation is constructed. Inserts for installation of anchor bolts are embedded in upper surfaces of the mat slabs 1, and construction members are directly constructed on mat foundation. Cut parts 5 for ventilation, step 6 for takingoff shoes ventilation holes, or recesses for housing devices to be installed may be provided in the mat slabs 1.