Abstract: Abstract: The decomposition of corn stalks returning to soil is very difficult. It has been the hot topic as to how to accelerate the decomposition of corn stalks in soil around the world. Isolation of cellulose-decomposing bacteria or fungi was conducted using the method of cellulose-Congo red stain in soil with straw returning which was collected from wheat-corn rotation farmland in Hebei province. The ITS genetic sequence of the strain determined by PCR was of 99% homology with that of Penicillium oxalicum when compared with the known sequence in the NCBI database using pairwise BLAST. The isolated strain was identified as Penicillium oxalicum on the basis of its morphological characteristics and ITS genetic sequence analysis and preserved in the China General Microbiological Culture Collection Center (CGMCC) with the preserved number of CGMCC NO.4842. The ability to decompose corn stalks and the conditions to produce enzymes by this strain were studied further. The results showed that the enzymatic activities of CMC and FPA were 672.8, 282.9 and 774.6, 618.3U when the strain was growing in the sodium carboxymethyl cellulose (CMC-Na) medium and corn stalks in the medium at 30℃ for 72h, respectively. The total activity of cellulose on a corn stalks medium reached to 376.1U. Moreover, the optimum conditions for enzyme production were 3% beef extract peptone as the nitrogen source, 5% of inoculated level , 28-35℃, pH =4-7 and cultured for 48-96 h. The best combination of pH value, temperature, solid-liquid ratio, and incubation time was pH value=6.5, 30℃, solid-liquid ratio at 1:10, and incubation for 48h. When the strain was cultured with powder of corn stalks in a growth medium for 10 days, 87.3% of the corn stalks were decomposed and 1.90 times higher than that in the control. When the strain was incubated in soil with corn stalks for 30 days, the decomposition rate was 83.5% and 1.62 times higher than that in the control. Finally, the wheat pot experiment was carried out to investigate the effect of this strain on corn stalks decomposition in soil when the plant was grown for 50 days. The result showed that the straw decomposition rate was 70.8% and 15.1% higher than that in the control. In conclusion, the strain of Penicillium oxalicum isolated from the soil with straw returning could decompose the corn stalks efficiently.