A method and system for interconnecting an Internet protocol version 4 (IPv4) network and an Internet protocol version 6 (IPv6) network are provided. The system for interconnecting an IPv4 network and an IPv6 network includes IPv4 nodes, IPv6 nodes, and apparatuses for transmitting IP packets between the IPv4 nodes and the IPv6 nodes, wherein the apparatuses for transmitting IP packets share processing state information of the IP packets, using a predetermined message, to distribute their load of processing the IP packets. The IPv4-IPv6 interconnection method involves appropriately arranging NAT-PT apparatuses depending on the size of the networks such that packet processing speed and performance are improved over the use of a single NAT-PT apparatus.