The design, construction, and field testing of an unmanned aircraft system to monitor high altitude volcanoes is described in this paper. The system must be able to fly above the crater of the volcano and acquire important information such as images, video, and concentration of gases in order to assess potential risks to nearby population. The system must be able to fly above 6000 meters above sea level autonomously with telemetry data transmitted up to 7 km away. All aspects of the system were developed considering the extreme conditions at which the aircraft was subjected. Field experiments were accomplished on two volcanoes in Peru, being one of them currently under eruption.