An airborne γ-ray spectrometry system that can be installed on an unmanned aerial vehicle (UAV) was designed to satisfy the requirements of radioactive mineral exploration and environmental radiation monitoring. The system consists of an airborne measurement device and a ground control platform. The airborne measurement device includes a γ-ray spectrum survey instrument, the main controller, data and graph transmission module. The ground control platform integrates the data and graph transmission module, industrial computer, energy spectrum analysis and processing software. Field flight tests showed that the data collected by the system were stable and reliable, and the survey results were consistent with existing data. The designed system can be applied to small-scale radioactive geological surveys, environmental surveys, and radioactive pollution monitoring.