In wireless sensor networks (WSNs), multihop routing protocols can achieve energy efficiency for data aggregation. However, the network lifetime still suffers degradations owing to the unbalanced energy consumption for all nodes. Therefore, in this paper, with an energy-saving scheme, we propose an improved cross-layer algorithm for media access control (MAC) and routing protocols. The proposed cross-layer algorithm allows more nodes to share the load of the leader of data relay and balance the opportunity of data relay to all nodes, in which the proposed load-balancing scheme allocates the energy consumption load more uniformly among all nodes. Thus, the lifetime of the first node death (FND) can be clearly prolonged. An analysis is carried out to show the energy efficiency of the proposed cross-layer algorithm. Simulation results show that the proposed scheme can prolong the lifetime of WSNs to be double the lifetime of FND compared with that using the shortest hop routing tree (SHORT) scheme.