P2P (Peer to Peer) is becoming a key technology to realize virtualized computing fields using the pervasive deployment and high-speed connectivity of computers through the Internet. However, P2P systems tend to waste the network bandwidth for resource acquisition because of its decentralized resourcemanagement. This paper proposes an efficient self-organizing overlay network for P2P-based grid computing systems to effectively reduce the number of resource-acquiring queries over the physical network. The resource exploitation space for some specific interests is organized as an overlay network, which is configured by making local clusters reflecting current interests of individual peers and connecting them together based on their similarity. In addition, the overlay network can be dynamically reconfigured based on the change in the interests of individual peers across time so that more useful peers at that time can be reconnected closer to their client peers. Therefore, multicasting of resource requesting messages can be carried out only over peers with similar interests that are connected through the overlay network. Experimental results indicate that the self-organizing overlay network can remarkably decrease both messages for resource acquisition and hops a resource requesting query travels to reach the peer that satisfies the request.