The forest fire monitoring is a new application of unmanned aerial vehicle (UAV). An introduction is made to a miniature UAV system for forestfire monitoring. It is composed of three parts: the miniature meteorological UAV, the digital image system (including two CCD cameras and a set of RF transmitter), and its software. In the test flight, the system successfully detected the fire targets on the ground. It is proved that the system has the ability to accomplish forestfire monitoring mission within a radius of 30 km (about 80 to 100 km2). The application of UAV in forest fire prevention is lowcost, feasible and promising. Some problems encountered the system development are discussed.