This paper describes the design procedure of a convertible miniature (mini and micro) quad tilt rotor unmanned air vehicle (UAV), which has about 2 meters of wing span, one hour of mission time and 5 kilograms of total weight. The aircraft is driven by four brushless direct current motors, and the structure of it completely made of composite materials. When the wing and tail of the aircraft are dismounted, it operates as a quad- rotor with tilting rotors. The aircraft is planned to carry a gimbal camera weighing about 700 grams. The primary operation areas of the aircraft are intelligence, surveillance and reconnaissance missions in an operational radius of 15 km. The aircraft is capable of changing its flight modes between horizontal and vertical flights as required by the mission profile.