Disclosed are a method and a device for operation based on a power save mode in a WLAN. The method for operation based on a power save mode may comprise steps in which: an STA, which has been switched to an awake state, transmits a PS-poll frame to an AP on the basis of the transmission cycle of a beacon frame; the STA receives an ACK frame from the AP in response to the PS-poll frame; after receiving the ACK frame, the STA overhears a different BSS frame; and within a preset time upon overhearing the different BSS frame, the STA determines whether or not to maintain the awake state on the basis of whether or not a power management control frame has been transmitted from the AP.