The present invention relates to a wireless communication system and, more specifically, provides a method and device for transmitting/receiving a frame in accordance with the bandwidth thereof in a WLAN system. The method for performing a response process in a WLAN system according to one embodiment of the present invention may comprise: a step in which a first station (STA) transmits a frame requesting a response frame to a second STA; and a step in which the first STA awaits the response frame for an ACKTimeout interval. The value of the ACKTimeout interval may be determined differently according to the preamble channel bandwidth type of the frame.