An original asynchronous Ultra Wideband — Impulse Radio (UWB-IR) wireless location system for sensor network is developed and evaluated through experiments. The system enables wireless nodes to be located and communicated with simultaneously at low power and low cost. The proposed system does not need system synchronization. Each access point of the proposed location system measures the time difference between two signals' received timing: one is from target node, and the other is from an access point, the position of which is already known. Then the position of the target nodes is calculated by a pseudo Time Difference of Arrival (TDOA) method. We first introduce the system configuration and asynchronous TDOA method adopted in this system. Next, we estimate the received-signal-timing measurement accuracy of UWB-IR signal and evaluate it in experiments using prototype UWB-IR transceivers. Then we estimate the location accuracy by the horizontal dilution of precision (HDOP) metric and show the field trial results of using the prototype UWB-IR location system.