Disclosed is an uplink (UL) multi-user (MU) transmission method by a station (STA) in a wireless LAN (WLAN) system. The uplink multi-user transmission method by an STA in a WLAN system according to the present invention includes the steps of: receiving a trigger frame including resource unit allocation information for orthogonal frequency division multiple access (OFDMA) transmission; transmitting a UL MU physical protocol data unit (PPDU) frame, on the basis of frequency resource allocation information; and receiving an ACK frame for the UL MU PPDU.