Most applications based on wireless sensor networks (WSN) have devices with constraints of limited energy and computational/storage capabilities. The traditional security mechanisms are not desirable to these applications. A lightweight security and energy-efficient clustering protocol was proposed in this paper to solve the security problem in the clustering-based sensor networks. Firstly, a lightweight security algorithm is proposed to meet the security requirements, which reduces the communication overload by using the transmission key index. Secondly, in the process of clustering, the base station (BS) and cluster head (CH) use lightweight authentication procedure to verify the identities hierarchically, to reduce the risk of attacks from malicious nodes posing as BS or CH. Thirdly, the proposed protocol is analyzed in the aspects of security and energy consumption. Simulation results show that the proposed protocol not only enhances the network security but also improves the energy efficiency.