Apparatus and method of security communication in ipv4/ipv6 coordination network system

An apparatus and a method of security communication in an IPv4/IPv6 integrated network system are provided to enable IPv4/IPv6 nodes to identify a secret key although a packet is changed through an NAT-PT server by using ID information without IP address information. An apparatus of security communication in an IPv4/IPv6 integrated network system includes at least one first node and a second node(300). The first node generates a KEY-ID which identifies each secret key shared with at least one IPv4 node, and exchanges the IPv4 node with the KEY-ID in a security agreement process. The second node(300) generates the KEY-ID which identifies each secret key shared with the IPv6 node, and processes the security agreement process according to the secret key corresponding to the exchanged KEY-ID.