AbstractFractionation using concentrated phosphoric acid is a cost-effective pretreatment approach due to production of highly reactive amorphous cellulose under modest reaction conditions. Chinese white poplar biomass was used as feedstock. The effects of pretreating temperature and liquid/solid ratio of H3PO4/poplar (v/w, ml/g) on poplar fractionation, enzymatic hydrolysis efficiency (EHE), and supramolecular structural change were investigated. Only 31% (w/w, g/g) cellulose was retained in the solid phase at the higher liquid/solid ratio of 10:1 for 60 min, while 38 % cellulose was retained at 8:1. Temperature played an important role in lignin removal, xylan hydrolysis, and enzymatic hydrolysis, which may eventually influence cellulose conversion. More than 40% lignin could be removed after 60 min pretreatment at above 50 oC. A majority of the xylan hydrolysis could be detected in mixed rinsing liquid after 80 min pretreatment at 50 oC and liquid/solid ratio of 10:1. Up to 96.37% EHE could be obtained after 24 h enzymatic hydrolysis at 50 oC. The optimal pretreatment condition was 50 oC, liquid/solid ratio 8:1 (v/w), and 60 min. After pretreatment the CrI index decreased from 39.9 % to 27.7 %, suggesting a decrease of crystalline area percentage. Pyrolysis-GC-MS results of precipitated lignin indicated that nearly 48% of the lignin was phenolic, such that it can be used as a natural antioxidative material.