The present invention relates to a method of embodying a cooperation system between SEND and IPSec in an IPv6 environment. The cooperation system between SEND and IPSec in accordance with the present invention includes: receiving an authentication completion report message including a first IP address of a host whose authentication is completed by the SEND; generating new authentication information corresponding to the host and storing the new authentication information in a temporary storage area, if authentication information for the host is not present in the temporary storage area, wherein the authentication information includes the first IP address; and if an authentication check request message including a second IP address is received from the IPSec, checking whether the second IP address is present in the temporary storage area, and sending the result of checking to the IPSec. The present invention allows the authentication information shared between SEND and IPSec in a mobile environment, where the network is frequently accessed, enabling IPSec secure communication at a lower cost.