A high-performance liquid chromatography method of pre-column derivatization with 1-phenyl-3-methyl-5-pyrazolone (PMP) has been established for determination monosaccharides composition of polysaccharides purified from Lactarius deliciosus. The optimisation of the pre-columnderivatization process were: reaction time of 40 min, reaction temperature of 70°C and PMP concentration of 0.8 M. HPLC conditions were as follows: Agilent Zorbax SB-C18 column; using phosphate buffer (0.05 M，pH = 6.9)-acetonitrile as mobile phase; detection wavelength 250 nm; injection volume 10 μL; column temperature 20°C. The determination results had good linear correlations with R2 ≥ 0.9996), good accuracy (RSD ≤ 2.23%) and repeatability (RSD ≤ 2.11%), and the recovery rate was in the range of 97.16-101.68%. This method could precisely determinate monosaccharides composition of polysaccharides purified from L. deliciosus.