An ultra-high performance liquid chromatography-tandem quadrupole mass spectrometric method was developed for the determination of monosaccharide composition and content in Mesona Chinensis Benth polysaccharides.Mesona Chinensis Benth Polysaccharides were extracted with hot water under alkaline environment,cleaned with C18 SPE cartridge,and then hydrolysised with trifluoroacetic acid at 110 ℃.The monosaccharaides were derivated with 1-phenyl-3-methyl-5-pyrazolone(PMP),and separated at a flow rate of 0.5 mL/min on a Waters ACQUITY UPLC BEH C18 column(2.1 mm i.d.×50 mm,1.7 μm) at 35 ℃,by using acetonitrile and 0.5 mmol/L ammonium acetate-0.05% acetic acid buffer as mobile phase by a gradient elution.The analysis of target compounds was performed in multiple reaction monitoring(MRM) mode via positive electrospray ionization,and quantified by the internal standard method.The developed method showed good linearities over the concentration range of 1-100 μmol/L for all monosaccharaides with correlation coefficient(r2) more than 0.96.The spiked recoveries were between 84% and 112%,and the relative standard deviations(RSD) were no more than 4.7%.The results showed that Mesona Chinensis Benth polysaccharides consisted of eight monosaccharides,including mannose,rhamnose,ribose,glucuronic-acid,galacturonic-acid,glucose,galactose,xylose,with the molar percentages of 7.4%,5.7%,4.2%,0.9%,28.4%,26.5%,16.4% and 10.6%,respectively.The method is simple,rapid,sensitive and convenient,and could be applied in the analysis of Mesona Chinensis Benth polysaccharides.