The present invention relates to a method for accessing channels in wireless communication systems and to an apparatus for same. More particularly, the method for supporting channel access of a station (STA), which does not belong to a group indicated by a traffic indication map (TIM), includes the steps of: receiving a channel access frame for requesting channel access within a TIM interval from an STA; and transmitting to the STA a response frame including information on whether to allow channel access of the STA in response to the channel access frame, wherein the channel access period of an STA, which belongs to the group, is determined on the basis of a bitmap of the TIM within the TIM interval, and the channel access of the STA is allowed only in a period other than the channel access period of the STA, which belongs to the group.