This study examined the optimal conditions for the oxalic acid pretreatment of yellow poplar for ethanol production depending on the combined severity factor (CSF). The factors affecting the ethanol fermentation of the hydrolysate were also analyzed. Xylose was the most abundant compound (2.80-16.44 g/L) in the hydrolysate, whereas the concentration of glucose was relatively low at 1.65-3.69 g/L. Ethanol production was highest at CSF 1.22 (10 min, 41 mM) after fermentation for 96 h, which resulted in a theoretical yield of 74.51% and an ethanol productivity of 0.027 g/L·h. The concentration of fermentation inhibitors (acetic acid, furfural, and total phenolic compounds) increased with increasing CSF. Ethanol production decreased significantly with increasing concentration of fermentation inhibitors at CSF higher than 1.59. The xylo-oligomer concentration was highest (18.77 g/L) at CSF 0.72, and the concentration decreased at CSF 1.52. The average molecular weights of the hydrolysate decreased slightly with increasing CSF. The degradation products contained in the hydrolysate were detected by gas chromatography-mass spectrometry. Among these products, the concentration of vanillin and syringaldehyde increased rapidly at high CSF.