在無線感測網路(wireless sensor networks, WSNs)上，許多應用需求感測器的位置，於是定位問題便成為一個基本且重要的研究議題。近幾年提出的方法中依距離知道與否可分為測距法(range-base method)和無測距法(range-free method)兩種，其中方向性天線鮮少被用在無測距法上。這篇論文，我們提出一個以方向性天線為基礎的無測距演算法，讓可以隨時得知自己位置的移動式錨節點(mobile anchor node)週期性使用方向性天線廣播訊息，而欲獲取自己位置的一般節點(normal node)只要接收訊息並以此計算出位置，以此減少錨節點的需求並降低成本。在本篇論文中，我們以方向性天線的特性改善大部分定位方法需要等到移動式錨節點通過兩次後才可定位的問題，提出讓一般節點在移動式錨節點走過一次後便可定位的方法，增加定位的精確性且降低計算複雜度。 Localization is a substantial issue for wireless sensor networks. The existing localization algorithms can be divided into range-based and rang-free methods by the range is awarded or not. Range-based methods are unsuitable in wireless sensor networks because they require specific device. In contrast, range-based methods do not need to measure the range information and only use simple and cheap hardware to localize. Although lots of range-free localization algorithms have been proposed, they seldom use directional antenna to improve. In this paper, we introduce a localization algorithm which uses mobile anchor nodes. Each anchor nodes can get their positions by Global Positioning System (GPS) receiver at any time. Anchor nodes move around the sensing field and broadcast beacons periodically by directional antenna. Normal nodes which want to know their positions can just listen and calculate by the information inside receiving beacons. It can lower the density of anchor nodes and decrease the computation complexity. By using the directional antenna, normal nodes can be localized in one pass of an anchor node and improve the accuracy of previous works.