A key structure comprises base plate, elastic member, frame and cap wherein the conductive membrane thereof is single-film structure, the contact of the conductive membrane corresponding to each key is of meshed-hook shape (), a venting aperture is provided at the center of the contact. A transparent and insulating layer is arranged upon the conductive membrane to prevent the short circuit of the circuit in the conductive membrane. An opening is provided at the transparent and insulating layer and corresponding to the conductive membrane. Both ends of the elastic member are attached to the cap and the transparent and insulating layer by adhesive. A conductive bump with a conductive layer is provided on the elastic member such that the conductive bump of the elastic member is connected to the contact of the conductive membrane and a closed loop is formed within the key when the cap is pressed down, whereby the signal generated by key stroking action is transmitted to the computer. The conductive membrane is designed to be single-film structure, whereby the keyboard is more compact with reduced height.