Disclosed is a session handoff method of an access terminal (AT) in a high-rate packet data (HRPD) mobile communication system. The session handoff method comprises performing a close procedure of a session in negotiation upon receiving a close request for a session negotiation from the AT performing session handoff; allocating a new unicast access terminal identifier (UATI) to the AT upon receiving a request for allocation of a new UATI from the AT after the session close procedure; and acquiring prior session information from a source session controller using an old UATI included in received prior session information upon receiving configuration information including the prior session information from the AT after allocating a new UATI to the AT.