A 30-kg-class ducted fan UAV has been developed in this study, which has two ducted fans and one tail rotor. The transmission system, including several gearboxes, was designed for driving ducted fans by a combustion engine. For the attitude control of this UAV, a control concept has been proposed. The aerodynamic performances of ducted fan in hover condition have been investigated with the unsteady CFD method and ground test. A full-scale prototype was fabricated and hover flight tests have been carried out.