Hydrazine monopropellant thrusters are used as propulsion system for trajectory corrections and other operations of satellites or unmanned spacecrafts. But hydrazine is difficult to handle, therefore the design and the synthesis of next generation monopropellants that could be able to supersede hydrazine is currently studied by scientists around the world. In this study, we focus on liquid glycidyl azide polymer (GAP) as next generation monopropellant. GAP is a liquid and stable substance at standard temperature and pressure. GAP is self-reacting with exothermic decomposition, however, the decomposition of GAP single droplets when heated was not investigated. To clarify the decomposition of GAP single droplets, we examined their decomposition behavior. It was found that GAP single droplets changed their status at certain temperatures in a furnace. Bubbles were generated at temperatures over 493 K, and micro explosions occurred at temperatures above 603 K. The temperature in GAP single droplets rapidly rose when micro explosions occurred. Moreover, the activation energy was obtained from the results of micro explosion delay time and of DTA. It was found that GAP is able to easily generate micro explosions by a small amount of energy.