Aspergillus rager NRRL 337, a significant lipase producer, also produced esterases in a semisolid medium. From the culture extract, four esterases (Esterase-I, -II, -III, -IV) were purified by means of ion-exchange chromatography, gel nitration, gel permeation with high performance liquid chromatography, and preparative disc gel electrophoresis. Homogeneity of each esterase was confirmed using disc gel electrophoresis. The four esterases were found to exhibit low isoelectric points (pH 3.63.9). The molecular weights determined by gel permeation chromatography of Esterase-I, Esterase-II, Esterase-III and Esterase-IV were 23000, 127000, 29500 and 27000, respectively.