Abstract: As an important issue in wireless sensor networks, localization is widely used to acquire node’s location in many aspects such as some routing mechanisms, target tracking, load balancing, topology control and so on. Traditional localization schemes need to pre-deploy a certain amount of static beacons in the network and the percentage of static beacons will directly affect the final localization result. In contrast, localization by use of mobile beacons is inherently more accurate and cost-effective. This study proposes a new ranging-free localization scheme with dual mobile beacons for wireless sensor networks. By deploying two fixed spacing mobile beacons moving in line with constant speed but different communication reach range, the localization can be realized through a single interaction with the unknown node. Since there is only few messages exchanged between unknown node and mobile beacons, this scheme is easy to control the node energy consumption. Furthermore, free from the channel noise interference is another key feature of this scheme due to the ranging-free technology. The simulation results have shown that the proposed scheme has good localization accuracy when mobile beacons themselves are localized with small error and beacon message transmit interval is reasonable.