In this paper, an instance-oriented security mechanism is proposed, to attack possible security threats in grid-based mobile agent system. The proposed delegation profile allows application systems to define their own security instances, while it provides mechanisms to delegate one?s identity on those instances, instead of on certain hosts, just like the conventional delegation does. This can prevent the delegated host from abusing privileges. By adopting the new delegation profile as a kernel, a new trust framework is then proposed to enhance the security verification ability and provide more fine-grained authorizations to mobile agents platforms.