A comparison study of a spray flash desalination process with the direction of injection based on experimental results of upward jet flash evaporation is presented. Superheated liquid at 24.0, 30.0, and 40.0 degrees C was injected upward into a depressurized chamber through a stainless steel cylindrical nozzle to compare with the phenomenon of a downward jet flash evaporation method. A series of experiments were carried out to analyze the effect of the direction of injection against the spray flash evaporation phenomenon. The tube-type nozzle was used with an internal diameter of 20.0 mm and a length of 81.3 mm. The range of the mean velocity of the superheated liquid inlet was from 1.74 to 3.62 m/s. The temperature descent of the superheated liquid inlet along the nozzle axis was measured by thermal resistance. Furthermore, the data and empirical equation for the downward jet method previously reported were used to compare the experimental results on the upward jet method. As a result, a tendency that the upward jet method needs a shorter distance to complete the flash evaporation than the downward jet method was observed. Therefore, the upward jet method has the possibility of making the spray flash desalination system more compact and efficient.