Wireless sensor networking, an emerging new field in technology, now opens a vast horizon of application scenarios including environment monitoring, home security and earthquake warning. Since the sensor nodes have limited available power, energy conservation is a critical issue and developing an energy-efficient routing protocol is one of the major issues in wireless sensor networks. In this paper, the authors propose a novel hierarchical routing protocol called Efficient Power Management Protocol with Limited Cluster Size (EPMPLCS) which limits the size of clusters and avoids large energy consumption among cluster-heads and distant members in big clusters thus prolongs the network lifetime. Furthermore, EPMPLCS improves the assumption that the data of different sensors in one cluster are highly correlated. Simulation results show that EPMPLCS performs better than Low-Energy Adaptive Clustering Hierarchy (LEACH).