In Opportunistic Mobile Networks (OppNets), a large amount of energy is consumed by idle listening, instead of infrequent data exchange. This makes energy saving a challenging and fundamental problem in OppNets, since nodes are typically battery-powered. Asynchronous duty-cycle operation is a promising approach for energy saving in OppNets, however, if its working schedule is not effectively designed, it may also cause significant network performance degradation. Therefore, it is pressing to design an energy-efficient working schedule for duty-cycle OppNets. In this paper, we first analyze the contact process in duty-cycle OppNets, then propose an adaptive working schedule for duty-cycle OppNets. The proposed schedule uses the past recorded contact histories to predict the future contact information, so as to adaptively configure the working schedule of each node in the network. Finally, extensive real trace-driven simulations are conducted to evaluate the performance of our proposed schedule. The results show that our proposed adaptive working schedule is superior to the random working schedule in terms of delivery ratio and delivery delay. © 2013 IEEE.