Abstract: A lipase from Aspergillus oryzae As-W6 was purified to homogeneity by ammonium sulfate precipitation,dialysis, DEAE- 52 cellulose column anion exchange chromatography and Sephadex G- 75 gel filtration chromatography. The purification protocol resulted in a 86.7-fold purification with a yield of 23.2%,the relative molecular weight of the purified lipase was 40.8 ku. The optimum temperature and p H of the purified lipase was 40 ℃ and 7,respectively. The lipase was stable over ranges of p H(6~8) and under the temperature 40 ℃.The lipase activity was enhanced by Ca2 +,Mg2 +and Acetone,while inhibited by Cu2 +,Fe2 +,Mn2 +and SDS. It achieved maximum values when soybean oil used as substrate, which indicated that the lipase showed a significant specificity toward soybean oil.