A foldable keyboard for a portable computer includes a keyboard body which comprises two keyboard pieces hinge-coupled by a hinge unit in order to be unfolded in a direction parallel to a keyboard plane. Another embodiment of the invention is a foldable keyboard, which includes: a guide unit at which a long hole is formed along its length; and a keyboard body which comprises two keyboard pieces hinge-coupled to the guide unit by a hinge unit. The keyboard pieces can be unfolded in a direction parallel to a keyboard plane into its extended state. As the keyboard pieces unfold, the hinge unit slides along the long hole as the keyboard edges, which are facing each other, are stuck together. Thus, the two keyboard pieces are hinge-coupled to each other to reverse their vertical and horizontal directions as the keyboard body is extended.