Abstract: The effects of steam explosion (2.5 MPa, 200 s) and Aspergillus oryzae fermentation on corn straw degradation were evaluated according to the changes of compositions and enzyme activities in the fermented products. The results showed that the steam explosion pre-treatment for corn straw could make the degradation rates of cellose, hemicelluloses and lignin reach to 8.47%, 50.45% and 36.65%, respectively (P<0.05). After pretreated with steam explosion the corn straw was fermented by Aspergillus oryzae for 6 days, the contents of cellulose and hemicellulose in the fermented corn straw were decreased by 27.89% and 64.80% respectively, compared with the original corn straw (P<0.05). The filter paper cellulase, CMCase, amylase and protease protease protease; protease activities in the fermented products were 335.10, protease protease protease; 1?138.92, 1954.20 and 201.99 U/g, respectively. Pre-treating with steam explosion and followed by Aspergillus oryzae fermentation seems to be a prospective method for corn straw degradation and application.