This document proposes an energy efficient clustering protocol for wireless sensor networks called LEACH-P that uses particle swarm optimization (PSO). It aims to improve the existing LEACH protocol by using PSO to select cluster heads in a way that maximizes the residual energy of nodes. The key contributions are applying PSO to select optimal cluster heads based on residual energy, simulating the proposed LEACH-P protocol and comparing it to LEACH to determine if it improves network lifetime, stability period and data transmitted to the base station.