Four forms of acid phosphatase, designated as Ia, Ib, IIa, and IIb according to their elution profiles of column chromatography, were isolated from the solid culture of Aspergillus oryzae. Ia and Ib were mainly produced in phosphate-enriched conditions, and conversely IIa and IIb were formed chiefly in phosphate-restricted conditions. The relation of enzymatic properties between Ia and Ib, or IIa and IIb were very similar, but Ia and Ib could be clearly differentiated from ha and lib. pH optima were about pH 4 for Ia and Ib, and about pH 6 for ha and IIb. Fluoride was a potent inhibitor for Ia and Ib, but not for ha and IIb. These enzymes seem to be non-specific acid phosphatases, phosphoserine, phosphothreonine, and phosphoethanolamine being hydrolyzed with IIa and IIb but not with Ia and Ib.