The mechanisms of action of phosphate solubilization were studied in the wild-type strain Aspergillus tubingensis and the phenotypic mutants derived from it. The P solubilization activities of these isolates were measured in liquid media using different carbon and nitrogen sources. All the mutants showed higher P solubilization compared to the wild type. Glucose and sucrose significantly promoted P solubilization compared to fructose, lactose, galactose, and xylose. Potassium nitrate significantly increased P solubilization compared to other nitrogen sources such as ammonium sulfate, ammonium nitrate, aspargine, and tryptophan. The P solubilization activity was strongly associated with the production of organic acids, especially succinic acid and acetic acid. The enzyme activities such as acid phosphatase and phytase also increased significantly in mutants compared to the wild type. These results suggested the role of these enzymes in P solubilization apart from the organic acid exudation and H+ pump in A. tubingensis.