The present invention relates to a method for operating a power save mode in a wireless LAN system. The method involves transmitting a power save multi-poll (PSMP) frame containing a power save mode (PSM) of a non-access point (AP) station (STA) to a first station and to a second station which are paired with an AP on the basis of multiple input multiple output (MIMO) technology. Information on the PSM contains downlink transmission start offset which indicates the point in time of starting a downlink transmission period, a downlink transmission duration which indicates the duration of the downlink transmission period, and transmission object station identification information. The method further involves transmitting a data frame to the first station and to the second station on the basis of the MIMO technology during the downlink transmission period. The transmission object station identification information indicates a group identifier (group ID) for indicating an object station group including the first station and the second station, which are object stations to which the AP transmits the data frame on the basis of the MIMO technology.