Aspergillus niger treated with ethyl methane sulfonate and gamma rays was incubated with samples of rock phosphate taken from Rajasthan, India for exploring its solubilisation capacity and phosphatase activity. 4 percent glucose and 0.4 percent sodium nitrate were the best carbon and nitrogen sources respectively. 0.1 percent KCl and 0.03 percent KH2PO4 stimulated the solubilisation process whereas CaCO3 inhibited it. Phosphatase activity was found to vary directly with the solubilisation process indicating that the dephosphorylation of the rock was due to the production of acid phosphatase enzyme.