This paper considers the localization problem of sensors in mobile wireless sensor networks. It proposes a combined localization technique, using both fingerprinting and accelerometer information. The proposed approach consists of two phases. In the first one, a power map is constructed over the surveillance area. In the second phase, nodes are localized and a first position estimate is computed using the constructed power map. A second estimate is also given using accelerometer information. Both estimates are then combined using interval analysis, solutions being boxes including the real positions of the nodes. Simulation results show that the combined method improves the positioning performance, compared to methods based only on fingerprinting or accelerometer information.