IPv6 is a new version of the Internet protocol, designed as the successor to IPv4. Among the changes from IPv4 to IPv6, we focused on the stateless address auto-configuration mechanism. The address auto-configuration mechanism is used by nodes in an IPv6 network to learn the local topology. The current specifications suggest that IPsec AH may be used to secure the mechanism, but there is no security association during address auto-configuration process because it has no initial IP address. As there are so many suity threats, SEND protocol was designed to counter these threats. In this paper we analyzed the security problems in NDP and SEND protocol. So we proposed the Modified NDP mechanism using PKC and AC in order to solve these problems.