Energy efficiency is a major concern in wireless sensor networks. A zone-based unequal multi-hop clustering (ZMC) algorithm is proposed in this paper to balance the energy consumption and prolong the network lifetime of the network. By dividing the network into equal-distant rings and equal-angle sectors, the optimal cluster formation is obtained. In the cluster head selection phase, a distance-based communication cost function is designed for electing proper cluster heads. As a result, the local and global energy efficiency is achieved. Simulation results show the good performance of the algorithm for prolonging the network lifetime.