Objective To analyze the monosaccharide composition and the relative content of different alcohol precipitations of Panax japonicus polysaccharides.Methods The four components of Panax japonicus polysaccharides were isolated by stepwise ethanol precipitation method.The four components of Panax japonicus polysaccharides were hydrolyzed with trifluoroacetic acid (TFA) and derivated by l-phenyl-3-methyl-5-pyrazolo (PMP),respectively.The monosaccharide composition and relative content were analyzed using LC-FT-ICR-MS and HPLC-UV method.Results The four components of Panax japonicus polysaccharides consisted of glucose,rhamnose,galacturonic acid,galactose,arabinose,and glucose was the main monosaccharide.With the increase of ethanol concentration,the relative content of Ara increased gradually,as while the GalA decreased.Conclusions Precolumn derivation HPLC method was successfully applied for the determination of the monosaccharides in Panax japonicus polysaccharides,and there were differences in the four ethanol precipitations of Panax japonicus polysaccharides.The study can provide a basis for the separation of Panax japonicus polysaccharides.