Embodiments of the present invention provide a method and an apparatus for transmitting an acknowledgement frame in a wireless local area network. The method includes: generating an acknowledgement frame for a send frame, where the acknowledgement frame includes a short acknowledgement frame, and the short acknowledgement frame includes an STF, an LTF, and a SIG; and sending the acknowledgement frame. In the embodiments of the present invention, the short acknowledgement frame may not include a data unit, so that a size of the acknowledgement frame is reduced and an overhead of the acknowledgement frame is cut down, thereby improving interaction efficiency of the acknowledgement frame.