Aspergillic acid-degrading enzyme was extracted from the cells of T. koningii M102 grown on a medium containing aspergillic acid. The enzyme was partially purified about 36-fold by ammonium sulfate precipitation and chromatographies with DEAE-Toyopearl 650 M and Toyopearl HW 60 F. The degradation product of aspergillic acid was isolated from chloroform extract of the enzyme reaction mixture, and identified as 2-hydroxyimino-3-methyl-1-pentanal by comparison of the mass spectrum with that of a chemically-synthesized authentic sample.