The evaporation characteristics of water/n-decane emulsion droplet at various temperatures and pressures were experimentally observed. Emulsion fuel was made by adding pure water to the base n-decane fuel with a volume ratio of 0.2. Span 80 was used as a surfactant, and ultrasonification was conducted for the mixing process. The temporal variation of the droplet diameter was optically observed by using a high-speed camera, and the changes in droplet temperature were also measured. The evaporation process of emulsion droplets was divided into three stages, namely, droplet heating, inflation/puffing, and pure evaporation. As the ambient temperature increased, the behavior of droplet inflation shifted to puffing during the inflation/puffing stage. A decline in the inflation/puffing incidence rate was noted at high-pressure conditions. The evaporation rate during the pure evaporation stage and the overall droplet lifetime were affected by the ambient temperature but not by the ambient pressure. The inflation of the droplet mostly occurred at relatively lower temperature and pressure conditions; it changed to puffing, however, at higher temperature and pressure conditions.