A method of multi user multiple input multiple output (MU-MIMO) communication in a wireless local area network (WLAN) system, and a transmitting device therefore, are discussed. The method according to an embodiment includes generating an Aggregate-Medium Access Control Protocol Data Unit (A-MPDU) including an A-MPDU subframe which includes a Medium Access Control Protocol Data Unit (MPDU) delimiter field and an MPDU; and generating a Physical Layer Protocol Data Unit (PPDU) including the A-MPDU by using a guard interval. The guard interval is selected by the transmitting device among a short guard interval and a long guard interval. The guard interval used for the PPDU is selected to be the short guard interval when the PPDU is generated for a plurality of receiving devices, all of which support the short guard interval. The method according to the embodiment further includes transmitting the PPDU to the plurality of receiving devices.