Unmanned Aerial Vehicles (UAVs) have shown a tremendous potential in the past decade. These aircrafts have played a pivotal role in numerous military, observatory, surveillance and commercial applications. The goal of this project is to design and develop a UAV system focusing mainly on Avionics System of UAV. An onboard Avionics box is fabricated housing a range of sensors and processing units. The sensors? data is filtered and sent down to the ground control station via a wireless link operating in the ISM band. These sensors include absolute pressure sensor, differential pressure sensor, temperature sensor, health monitoring sensors, Inertial Measurement Unit (IMU) and GPS, etc. Control signals generated at the ground are sent to the airborne unit via the Telecommand link, also working in the ISM band. These signals are subsequently used to actuate the control surfaces of the aircraft. Extensive on-ground as well as airborne testing of the system is performed.