A method and an apparatus for receiving an ACK frame in a WLAN system are proposed. Specifically, a first STA transmits a plurality of first MPDUs in a first transmitting TDD slot to a second STA. The first STA receives a first ACK frame for the plurality of first MPDUs from the second STA in a first receiving TDD slot. The first STA transmits a second MPDU to the second STA in a second transmitting TDD slot. The first STA receives a second ACK frame for the second MPDU from the second STA in a second receiving TDD slot.