Abstract: The evaporation of single droplets containing various dissolved inorganic salts was studied experimentally. It was found that the drying process of most sample droplets in a high temperature gas stream comprised four rather than two periods, namely, (1) a constant rate period at wet-bulb temperature, (2) a falling rate period, (3) a boiling-evaporation period or constant rate period at the boiling point of the saturated solution and(4) a second falling rate period. Such a four-stage mechanism should be taken as a general one for the evaporation-drying process of droplets containing dissolved solid substances, and the disappearance of certain stages is but a special case under certain conditions. The effects of some variables such as medium temperature, initial concentration and initial diameter of droplet on the drying charateristics were investigated. The critical moisture contents corresponding to the turning points of various drying stages have been measured.