A novel biphasic organic solvent, 2-phenoxyethanol (EPH) was introduced to pretreat and fractionate rice straw into glucose/glucan, xylose/xylan and lignin under mild conditions. In addition, the combined severity factor (CSF) was used to evaluate the effect of pretreatment severity on the composition variation of rice straw. Under the biphasic system (0.05 M H2SO4, 70 % EPH:30 % H2O), 130 degrees C cooking rice straw 2 h, 86.48 % of cellulose retention in solid residue, 92.10 % of hemicellulose removal and 63.16 % of lignin removal were obtained. Then, the solid residue was enzymatically digested with a glucose yield of 80.94 % at 36 h, and the pure lignin (92.60 %) was recovered by simple precipitation. Based on the fractionation process, 96.69 % of glucose and glucan, 81.83 % of xylose and xylan, and 71.71 % of lignin in solid and liquid phase were recovered. Finally, the residue, especially the retrieved lignin was characterized by SEM, XRD, FTIR, HSQC and thermogravimetric analysis.