A new high Mr aminopeptidase was discovered and purified from Aspergillus oryzae grown on solid bran culture medium. The purified enzyme was homogeneous on polyacryl-amide gel electrophoresis (PAGE) at pH 9.4, and its Mr was 690,000 a gel filtration. The pI was 4.6. The enzyme was inhibited by ethylenediamineteraacetate (EDTA) and o-phenanthroline. It had a pH optimum at pH 7.5 for L-leucyl-glycyl-glycine (Leu-Gly-Gly). The Km value of the enzyme for Leu-GlyGly at pH 7.5 and 30℃ was 16.7mM.