A modular computer includes a main board unit, a power supply unit, a CPU, a graphic/display unit, a data reading/writing unit and a plurality of fasteners. Each of the units is formed into a rectangular six-face-boxed modular. A connector is provided on one of the faces of the units. The units are stacked in vertical direction or arranged in horizontal direction. The units are fixed together by the fasteners. The connectors provide electrical connection among the units.