A method for supporting handoff and preventing data loss in mobile communications networks is provided. The method for a mobile node establishing a mobile Internet protocol (MIP) with at least one or more wireless packet service systems, each of which has a serving GPRS support node (SGSN) and a gateway GPRS support node (GGSN), includes: a first SGSN connected to the mobile node transmitting predetermined first connection information on the mobile node to at least one or more second SGSNs adjacent to the first SGSN; the second SGSN receiving the first connection information storing the first connection information as a database item, and transmitting 1 first connection acknowledgement message to the first SGSN; if reception of the connection acknowledgement message is successful, the first GGSN connected to the first SGSN transmitting predetermined second connection information on the mobile node to at least one or more second GGSNs connected to the second SGSN; and the second GGSN receiving the second connection information and then transmitting a second connection acknowledgement message to the second GGSN. By transmitting information on a mobile node required for handoff to adjacent foreign agents (FAs) in advance, when handoff is performed, reliable handoff can be performed quickly without resetting and releasing a PPP, such that IP mobility services can be provided.