Disclosed is a data transmission method in a wireless network capable of improving transmission performance on a wireless network by transmitting data, on which ACK is piggybacked, using the ACK transmission opportunity having high priority. The data transmission method includes acquiring a wireless channel by a STA to transmit a first data to the AP, transmitting the first data by the STA acquired the wireless channel to the AP through the wireless channel, analyzing by the AP whether there are second data intended to any one of the plurality of STAs, and, if there are the second data to transmit, transmitting the second data, on which an ACK is piggybacked, to the intended STA from the AP using ACK transmission opportunity having higher priority than that of data transmission.