A wireless sensor network (WSN) is a group of wireless sensor nodes working together to sense the environment, perform simple data processing and communicate wirelessly. While mobile WSN is a type of WSN where the sensors are capable to move on their own to perform certain tasks. An important issue that affects the performance of WSN is the coverage problem. It concerns on how to ensure that the region of interest (ROI) is adequately covered by the sensors. In mobile WSN, coverage can be improved by moving the sensors so that a better arrangement is achieved. However, movement is a high consuming task therefore energy conservation is another important issue in mobile WSN. Here, a member of swarm intelligence family; particle swarm optimization (PSO) is used to solve coverage optimization and energy conservation problem in mobile WSN.