Provided is a method of segmenting a packet using a tree structure in order to reduce headers in the packet when the packet is transmitted or received in a wireless communication system using an adaptive modulation and coding (AMC), and a method of transmitting/receiving a packet using the same. The method includes the steps of: determining whether a transmitting processing data unit (PDU) is a retransmitted PDU; determining whether a size of the retransmitted PDU is a transmittable size allowed by a corresponding adaptive modulation and coding (AMC) option if the transmitting PDU is the retransmitted PDU; and segmenting the retransmitting PDU, inserting a header and a sub header with identification information for reassembling into each of the segmented PDUs and transmitting the segmented PDUs.