Nowadays, many buildings are equipped with a WLAN infrastructure, as an inexpensive communication technology. In this paper a method to estimate position and heading (pose) of a mobile robot using WLAN technology is described. The proposed technique for localizing a mobile robot is based on the use of received signal strength values of WLAN access points in range. A radio map based method and Euclidean distance in combination with Delaunay triangulation and interpolation is proposed. Measured signal strength values of an omnidirectional antenna and a beam antenna are compared with the values of a radio map, in order to estimate the pose of a mobile robot, whereby the directionality of the beam antenna is used to estimate the heading of the robot. The paper presents the experimental results of measurements in an office building.