A media access control (MAC) apparatus and corresponding methods for guaranteeing quality-of-service in a wireless local area network (LAN) are presented. The MAC method includes extracting, performing, determining, a first transmitting step, and a second transmitting step. The extracting includes extracting a user priority from a frame received from an upper layer and separately storing a voice frame and a non-voice frame according to an access category (AC). The performing includes independently performing backoff operations for the voice frame and the non-voice frame. The determining includes determining whether the backoff operations for the voice frame and the non-voice frame have simultaneously ended. The first transmitting includes transmitting the voice frame having a higher priority first and performing the backoff operation for the non-voice frame if the backoff operations have simultaneously ended. The second transmitting includes transmitting a frame whose backoff operation ends if the backoff operations have not simultaneously ended.