Abstract: A built-up watercraft includes a body consisted of three base boards hinged together and bilaterally supported on two floats by two wings, two propeller runners bilaterally coupled to a transmission mechanism mounted on the body at the back, a rudder assembly fastened to the body below the transmission mechanism, a steering wheel assembly mounted on the body at the front and driven to adjust the direction of the rudder assembly. The three base boards of the body and the wings are folded up and formed into the shape of a case as the watercraft is not in use. Connecting tubes are made on the wings and the body for permitting a plurality of watercrafts of the same structure to be connected in series as well as in parallel by flexible connecting rods.