A wireless network system and method to secure Quality of Service (QoS) according to a type of Wireless Local Area Network (WLAN) service in a WLAN communication system based on IEEE 802.11 includes: an authentication server adapted to set a priority for an access category of a wireless network service requested by a user to perform an authentication procedure in response to a user terminal requesting authentication for access to a wireless network; and an Access Point (AP) adapted to receive and store access category information of the user terminal authenticated by the authentication server and to compare access category information contained in a packet received from the user terminal to the previously stored access category information of the user terminal to control access to the wireless network.