Multiuser cooperative communication significantly improves the performance of wireless communication networks. One key challenge of multiuser cooperative communication is how to design a cooperative mechanism to incentivize potential relay nodes to help a source node in its data transmission. In this paper, to address this problem, a contract-based principal-agent framework is proposed in the context of cognitive-radio-based wireless relaying networks in which the sources’ wireless characteristics constitute hidden information which is not known by the relay. The problem is modeled as a monopolist’s problem, in which a mobile relay node acts as the principal who designs Incentive-Compatible (IC) and Individually Rational (IR) contract items, consisting of a set of rate-price pairs.