A method for processing session information of an Internet protocol voice call system using a session initiation protocol (SIP), extracting session information by parsing a SIP Session Protocol header (SIPSP Hdr) only without parsing a session initiation message, by stipulating a session protocol layer in the session initiation protocol and attaching a header of the session protocol layer to the session initiation message, thereby performing communication between a client and a server. The session protocol layer being formed between a UDP (User Datagram Protocol) layer and an SIP application layer.