Abstract: Three methods, namely extraction at constant pH value, alternative extraction using organic and inorganic solvents, and sequential extraction at different pH value, were adopted to separate 18 low-molecular-weight phenolic compounds from Eucalyptus urophylla kraft pulping black liquor. Using the method of sequential extraction at different pH value, i.e. sequential extraction at pH value 12, 7 and 2, total relative yield of low-molecular-weight phenolic compounds is 2 379.7 mg/L. The method not only avoids serious co-precipitation caused by the method of extraction at constant pH value, but also reduces loss of low-molecular-weight phenolic compounds caused by complicated procedures of the method of alternative extraction using organic and inorganic solvents. Moreover, co-precipitation rates of syringaldehyde, with acetosyringone (which can be used as natural mediators of laccase), and guaiacol with syringol (which can be used to synthesize polymers, phenoxyherbicides and biocides) are 38.65%, 43.31% and 12.25%, 14.81% for the method of extraction at constant pH value, but there is almost no co-precipitation for the method of sequential extraction at different pH values.