The development of smart devices has highlighted the need for human-device interaction. A key aspect of this interaction lies in the estimation of the physical orientation of the device, which is crucial for various applications. Conventional methods employing Inertial Measurement Units (IMU) encounter limitations such as cumulative errors and magnetic interference. In this paper, we propose UWBOri, a novel method for orientation estimation using Ultra-wideband (UWB) technology. UWB technology, which is increasingly integrated into smart devices, offers superior ranging accuracy owing to its large bandwidth. By leveraging the localization information obtained between a fixed UWB-equipped anchor device and the user device, UWBOri can accurately estimate the orientation of the user device. The efficacy of UWBOri has been validated through extensive laboratory experiments designed to evaluate the accuracy of orientation estimation. Furthermore, we demonstrate the practical applicability of UWBOri in two distinct scenarios: IoT device selection and augmented reality (AR). These applications illustrate the potential of our solution in real-world scenarios.