The present invention relates to a flat plate heat pipe and a method for manufacturing the same. The heat pipe includes a flattened pipe whose inner surface is coated with a wick structure layer. The interior of the flattened pipe is provided with a sintered supporting layer and a working fluid. The sintered supporting layer has a plurality of posts arranged in the flattened pipe to vertically support therein. With this arrangement, the thickness of the pipe can be reduced but the whole structural strength can be maintained to prevent deformation. Further, a return path for the working fluid can be provided in the pipe. By only sealing two sides of the pipe, a sealed chamber can be formed for the operation of the working fluid. By the inventive method, the manufacturing process can be simplified and a larger space inside the chamber can be obtained.