The present disclosure provides a circuit substrate, a method for manufacturing the same, a display substrate and a tiled display device. The circuit substrate includes: a base substrate; a driving circuit on the base substrate; and conductive connection portions. A plurality of grooves is defined in a lateral side of the base substrate; each of the plurality of grooves extends through a top surface and an opposite bottom surface of the base substrate. The driving circuit includes signal lines on the top surface of the base substrate and signal-line leads on the bottom surface of the base substrate. The plurality of conductive connection portions are corresponding to the plurality of grooves in a one-to-one manner; at least one part of the conductive connection portion is in the corresponding groove. The conductive connection portion is connected with the corresponding signal line and the corresponding signal-line lead, respectively.