The objective of this research was to extract polysaccharides from Isatis indigotica Fortune（INF） roots and determine their molar mass distribution.INF root powder was sequentially refluxed with petroleum ether and 95% ethanol to remove ether-soluble and ethanol-soluble components before polysaccharide extraction by hot water reflux.Polysaccharide content was quantified by phenol-sulfuric acid method and polysaccharide molar mass distribution was determined after hollow fiber membrane filtration for the removal of impurities.The content of ether-soluble and ethanol-soluble components in INF roots was 4.89%.Three repeated hot water reflux extraction for 1.5 h each time at a material-to-liquid ratio of 1：9（g/mL） for the first extraction and of 1：7 for the second and third extractions was found optimal for INF roots with and without the above pretreatments.The polysaccharide yields after the first,second and third extractions and total polysaccharide yield from pretreated INF roots were 7.34%,4.65%,3.12% and 15.11%,respectively and those from non-pretreated INF roots 6.51%,6.04%,5.69% and 18.24%.The molar mass distribution of polysaccharides from INF was mainly from 2 × 104to 5 × 104g/mol and polysaccharides with a molar mass from 1×104to 1×105g/mol accounted for 90.8%.The results indicate that INF roots planted in Daqing are rich in polysaccharides.The method developed in this study to determine the molar mass distribution of polysaccharides from INF roots is simple and reliable with the avoidance of tedious operations and experimental errors resulting from repeated separation and purification.%提取板蓝根多糖并测定其含量和摩尔质量分布。板蓝根生药粉经石油醚脱脂和95%乙醇多次回流提取（得到模拟板蓝根制药残渣）后,再用水提取多糖,用苯酚-硫酸法测定提取液中的多糖含量,以中空纤维膜分离除杂后的板蓝根多糖提取液并测定各分离液中多糖含量,计算多糖摩尔质量分布。结果表明：板蓝根生药粉中醚溶和醇溶物质质量分数为4.89%;连续水提3次、提取温度95℃、每次1.5h,第1次提取料液比为1：9（g/mL）,后两次均为1：7（g/mL）,3次提取多糖得率分别为7.34%、4.65%和3.12%,总得率15.11%;生药粉直接水提3次,多糖得率分别为6.51%、6.04%和5.69%,总得率18.24%;板蓝根多糖摩尔质量主要分布在2×104～5×104g/mol之间,摩尔质量在1×104～1×105g/mol范围内的质量分数为90.8%。大庆地产板蓝根中多糖含量丰富。多糖摩尔质量分布的测定方法简便、可靠,避免了反复分离、提纯带来的繁琐操作和实验误差。
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