Routing protocols for wireless sensor networks pay a great attention to the limited resources of the nodes. In this paper, we study LEACH routing protocol and its performance and propose a new protocol, MA-LEACH. We introduce a mobile aggregator which is a gadget adopted to mitigate the overhead on the cluster heads(CHs). In addition, we optimize the trajectory using particle swarm optimization (PSO). Hence, we adapt the TSP problem to our protocol to determine the optimal trajectory that a mobile aggregator could travel to visit every cluster head in the network. We simulate the proposed protocol in MATLAB and the results reveal that it outperforms LEACH in network lifetime and energy consumption. Also, we compare our findings with a recent extension to the LEACH called LEACH with fuzzy descriptors. The simulation results show that MA-LEACH surpasses LEACH with fuzzy descriptor.