AbstractAlkaline precipitate isolated from red liquor of acidic magnesium sulfite pulping exhibited obvious stratification. The properties of the stratified alkaline precipitate were investigated via infrared spectroscopy, ion chromatography, thermogravimetric analysis, and high efficiency liquid chromatography. The sulfonic group of lignosulfonate showed a characteristic absorption peak from 1210 cm-1 to 1170 cm-1. There were no significant differences between the structures of the functional groups of the upper and lower layers of the precipitate. The peak time of the sulfonic group was 6.350 min, as measured by ion chromatography. Compared with the upper precipitate, the lower precipitate had more groups with high carbon and low oxygen contents and did not easily decompose. The relative molecular weight of the lower precipitate was greater than that of the upper precipitate. The difference in relative molecular weight of the precipitates gave rise to the observed stratification.