A good query plan in p2p networks is crucial to increase the query performance. Optimization of the plan requires effective and suitable remote cost estimation of the candidate peers on the basis of the information concerning the candidates’ run-time cost model and online time. We propose a fuzzy reward model to evaluate a candidate peer’s online reliability relative to the query host, and utilize a real-time cost model to estimate the query execution time. The optimizer is based on the run-time information to generate an effective query plan.