A primary challenge faced by Wireless sensor networks is to transmit large chunks of data by sustaining the limited energy available. We propose to reduce the energy consumption of data-intensive WSNs using cheap mobile relays. Our proposal differs from previous work in that we integrate the energy consumption due to both mobility and wireless transmissions into an optimization framework. This framework consists of three main aspects. The first procedure computes an optimal routing tree with an assumption that no nodes can move. The second procedure involves adding mobile nodes using genetic algorithm (GA).The third procedure improves the network by optimizing the routing tree. This algorithm links up to an optimal position for each node, given that the topology of routing tree does not change. Our simulation results prove that our proposal significantly surpasses the existing solutions. © 2006-2017 Asian Research Publishing Network (ARPN). All rights reserved.