Provided are an apparatus and a method for scheduling contention-based data transmission in a network system including an access point (AP) and a plurality of terminals. The method includes determining a contention window (CW) size based on the number of terminals connected to the access point, and transmitting information about the contention window size to any one of the plurality of terminals. The apparatus includes a processor and an RF unit. Here, the processor is configured to determine a contention window (CW) size based on the number of terminals connected to the access point, and transmit information on the contention window size to any one of the plurality of terminals through the RF unit.