The use of portable computing devices has been booming in recent years. Making sure of the security in mobile systems has become a very important issue. A secure Mobile IP is designated to solve this problem, but it has suffered from a long delay caused by the mobile host frequently roaming to different agents in the same visited network. The new foreign agent must authenticate the mobile host via the mobile host's home agent. To reduce the overhead of authentication and home registration, we propose a secure Mobile IP registration scheme with hierarchical mobility management. We employ one-way hash function and symmetric cryptosystem to reduce the computation cost of authentication. Furthermore, we deploy a group key for each foreign agent, to simplify the authentication procedure between the mobile host and visited foreign agent.