Policy-Based Networking (PBN) became a key concept for the management of emerging Internet services. In fact the complexity of emerging QoS and security protocols make it very difficult to assure consistency in the configuration and performance management of IP infrastructure. Thus PBN assumes proactive management of the network based on high-level specifications of organizational objectives and goals. In this context, this paper aims to provide one possible interoperability solution between various policy domains based on mobile agent and policies. The objective is to automate as much as possible the negotiation process between the customer and its ISP and be tween ISPs. Each actor delegates responsibilities to a mobile agent. The mobile agent moves in the network from one PBN system to another in order to negotiate the service level requested by the customer or by a client ISP.