The objective of the invention is to provide a thin and flexible flat cable suited for being arranged in a narrow space such as a vehicle, as well as, a method for stably preparing such a flat cable. To attain the objective, there is provided a flat cable which has a plurality of conductors which is arranged parallel to each other, and an insulating layer disposed over the plurality of conductors by extrusion molding. The insulating layer has Melt flow rate value of 2.0 g/10 minutes or above at a molding temperature during the extrusion molding, and is formed of thermoplastic resin selected from the group consisting of polyolefin, polyphenylene ether, polyphenylene sulfide and a combination thereof.