Abstract: Abstract: The experiment was conducted to investigate the effects of steam explosion on water soluble pentosans mass fraction of wheat bran. The common commercial wheat bran was exploded by steam under the conditions as follows: the ratio of water to material was 20%, 30% and 50%, steam retention time was 30, 60 and 120 s per ratio of water to material, and steam pressure was kept at 2.0 MPa. Mass fractions of water soluble pentosans, total pentosan, neutral detergent fiber, acid detergent fiber and hemicellulose, and thermogravimetric curves were analyzed. The results showed that steam explosion could significantly increase the mass fraction of water soluble pentosans in wheat bran (P<0.05). Under the same steam pressure, water soluble pentosan mass fraction of the treatments through steam explosion could be increased with the lengthening of steam retention time (P<0.05), water soluble pentosan mass fraction under 60 s steam retention time could be increased by 9.0 times (P<0.05), and that under 120 s retention time could be increased by 10.1 times (P<0.05) compared with untreated wheat bran. Compared with untreated bran, steam explosion increased water soluble pentosans mass fraction at different degree with the increase of ratio of water to material (P<0.05), which could be increased by 9.4 times (P<0.05) at 30% ratio of water to material and by 6.5 times at 50% ratio of water to material (P>0.05). The mass fraction of total pentosans could be significantly decreased in wheat bran by steam explosion (P<0.05), and reduced by 62% (P<0.05) under the conditions of 20% water material ratio, 2.0 MPa steam pressure and 120 s steam retention time compared with untreated wheat bran. Considering the extraction efficiency and energy consumption, the better steam explosion conditions for water soluble pentosans were 30% ratio of water to material and steam processing for 60 s when steam pressure was kept at 2.0 MPa, and under these conditions mass fraction of water soluble pentosans could be increased by 10.8 times (from 1.3% to 13.9%), neutral detergent fiber could be decreased by 17.2% (P<0.05), hemicellulose decreased by 26.7% (P<0.05), activation energy of hemicellulose pyrolysis process increased by 21.5%, initial and end temperature were postponed by 19-30 ℃, temperature corresponding to maximum weight loss rate took forward by 13℃ and maximum weight loss rate reduced by 43%. This study demonstrates that steam explosion can significantly improve the mass fraction of functional active polysaccharides (water soluble pentosan) in wheat bran, which is helpful for deep processing and utilization of wheat bran.