A series of in vitro experiments were carried out to evaluate the effectiveness of a phosphorus-solubilizing fungus to desorb phosphate (Pi) from soil samples differing in their Pi-sorption capacity. The results indicate that the fungus Mortierella sp. was effective in desorbing Pi from all soil samples tested by producing oxalic acid, and its effectiveness varied among soil orders. The effectiveness of the fungus was influenced by the soil Pi-sorption capacity, which could be used as a predictor of the effectiveness of microbes to increase soluble Pi via desorption from soils. The Pi desorption was most pronounced in a Mollisol followed by an Oxisol, an Ultisol, and then by three Andisols. The quantity of Pi desorbed by the fungus was also greater when the amount of sorbed Pi was high.