Disclosed are a method and an apparatus for power save mode operation on the basis of a frame transmitted from another BSS in a wireless LAN. A method for operating an STA in a wireless LAN in a power save mode comprises: a step in which the STA receives a beacon frame from an AP, the beacon frame comprising a TIM element indicating downlink data pending in the STA; a step in which the STA transmits a PS-poll frame to the AP in response to the beacon frame; a step in which the STA receives, from the AP, an ACK frame transmitted by the AP in response to the PS-poll frame; and a step in which the STA determines the operation of the another BSS in a TXOP power save mode on the basis of the ACK frame.